[RPG] way to prevent a Forge Cleric from using Divine Intervention to escape from custody

Player's Handbook II (3.5) / Divine Conversion / p193

This is a sidebar at the bottom of the referenced page, which is part of a section on rules for retraining. If you don't have the book, here is the direct quote:

DIVINE CONVERSION

As noted in the Player’s Handbook, a cleric who grossly violates the code of conduct imposed by his deity loses all spells and class features and cannot attain any more levels as a cleric of that deity. All these penalties remain in effect until he atones. But what if he doesn’t want to atone? What if a cleric of Hextor finds new meaning and purpose in serving Heironeous after a dramatic conversion experience? Such a character need not become a multiclass ex-cleric of Hextor/cleric of Heironeous. Instead, Heironeous can simply reinstate the character’s cleric powers once he has proven his loyalty, talent, and ability.

A cleric who changes his patron deity must complete a quest to prove his devotion to his new patron. The nature of the quest depends on the deity, and it always clearly reflects the deity’s alignment as well as his or her goals and beliefs. To start the process, the cleric must voluntarily accept a geas/quest spell cast by a higher-level cleric of his new deity. During the quest, the cleric has no access to spells or cleric class features—except his weapon and armor proficiencies, which he does not forfeit.

Upon completing the quest, the cleric receives the benefit of an atonement spell from a cleric of the new deity. The character then becomes a cleric of the new deity and is inducted into the clergy during an appropriate ceremony of the DM’s choosing. After selecting two of the new deity’s domains in lieu of his old ones, the character has all the powers and abilities of his previous cleric level, plus the granted powers of his new domains.

This method is the only one by which a cleric can change his deity. The retraining rules can’t be used to accomplish this task—it is simply too substantial a change in the character’s identity (not to mention his source of power) to chalk up to a bit of practice in his off hours.

This answer essentially reflects the ruling already found in the Forgotten Realms Campaign Setting, but it may be useful to know it's also located in a setting-independent rulebook, just in case there are any sticklers out there.

It seems that your question is more about making your character's theme a viable play option, since you already have a fleshed-out idea for the flavor, theme, and personality of the character itself.

Being a Cleric, there are a few things to be aware of:

Spellcasting

You get spells and you get higher tiers of spells at every odd level (starting at level 1). You also have knowledge of all spells you can cast, but will only get to select a choice few each morning for casting throughout the day.

Also, your Wisdom stat is going to be associated with the irresistability of your spells (Spell Save DC) and the number of bonus spell slots you'll have at your disposal for each level.

Domains

You get two domains associated with your deity of choice. For each domain you get, you gain access to certain magical abilities which scale with your level to some extent. As a result of having domains, you also get a bonus spell slot for each level of spells that you can cast which can be used to cast a spell associated with either of your domains; these are called your Domain Spells.

For evaluations of which domains you should pick, you should look through a Cleric guide that touches up on domains.

Moderate Base Attack Bonus

There are three tiers of Base Attack Bonus progression. These denote your class' to-hit rating, attack accuracy, before any of your character's individual stats are included. Clerics have the Moderate tier, which towards Level 20 comes out to +15, five points behind Full Base Attack Bonus characters who get a full +20 BAB.

In the earlier levels, you'll only be 1 or 2 points behind these characters, and the difference in accuracy can be mitigated.

Favored Weapon

Because Erastil is your Deity, you are proficient in Longbows. Otherwise, a Cleric is only proficient in simple weapons (which a longbow is not).

Feats for Archery

Feats are the building blocks which distinguish your character from other characters of your same class in terms of what they can do. These are generally mechanical advantages, passive stat boosts, or unique types of actions only the feat bearers can accomplish.

There are actually quite a number of feats which get taken by most archers.

Point-Blank Shot
This feat grants +1 to attack and damage with ranged weapons within 30 ft. Often, combat happens close, even if you're an archer.

Precise Shot
This feat requires Point-Blank Shot. It solves a major penalty to archery combat: shooting at targets which are hostile to each other and are within smacking-distance of each other nets YOU, the archer, a -4 penalty to attack. This feat removes that penalty.

This penalty is a problem because your targets will often be fighting with your allies in melee. You'll want this just to avoid inaccuracy in this very common situation.

Rapid Shot
This feat requires Point-Blank Shot. It allows you to trade accuracy for an additional attack. At the cost of reducing your attack rolls by -2 for the round, you can shoot an additional time.

This feat provides benefits two-fold: (1) by shooting twice, you're more likely to hit at least once and (2) if you hit twice, you deal your damage twice. Later on, you'll get additional attacks when your BAB hits +6 and +11, but the extra attack from Rapid Shot is more valuable because it's at your full Attack Bonus -2, where as the others you gain will be at -5 and -10, respectively.

Later on, getting Manyshot will be an option for continuing this feat line.

Deadly Aim
This is another feat that allows you to trade accuracy for something. In this case, it's damage. At the cost of -1 attack for each +2 damage the feat provides, you're getting attack damage that scales with level.

Normally, this feat is one picked up by Full BAB characters without question, but it requires consideration for lower-BAB characters since the trade may not be as valuable to them in terms of expected damage output.

To decide when to use Deadly Aim, you can do some math:

• Take your average damage on a hit, call it \$x\$.
• -1 to Attack is equivalent to doing \$\frac{x}{20}\$ less damage on average.
• Take your chance to hit as a decimal, call it \$y\$.
• +2 to Damage on hits is equivalent to doing \$2y\$ more damage on average.

In the fresh early game, you'll likely want to focus on Attack Bonus, even if your average damage increases from the trade. Those are the levels where hitting or missing are most crucial, and you'll likely be dealing finishing blows with less damage. However, later on, the bonus damage is integral to ending a combat.

Weapon Focus (Longbow)
This feat gives +1 to attack bonus with Longbows. This feat is one you should definitely pick up if accuracy becomes an issue. that exists.