How to increase the bond level for buddies

The Skulls can be avoided in their first appearance (Resucing Miller / Phantom Limbs) with a little bit of patience.

First, use your IntScan to mark all 4 Skulls -- two at the top of the bridge, and 2 along the slope to the left of it.

Now, you wait. The skulls will slowly shamble forwards, with the left skulls going down the slope, and the right skulls approaching and then beginning to go down the slope on the far side of the bridge. Your approach should be straight across. Once the right-pair has started down the slope, make your move. You have a rather narrow window where the Right skulls are far enough down the slope to break line of sight before they come back up the hill and camp the edge of the bridge.

Once you're a good 100m on the far side of the skulls, feel free to whistle up D-Horse, fling Miller over his back, and casually ride the rest of the way to the extraction site.

Edit:

Alternatively, change the helicopter's landing zone. If you take out the radar dish, you can have your chopper land right outside the prison. (Just make sure the guards are unavailable/incapacitated!)

There are a couple of things involved in having your helicopter play music out loud.

First, you must develop a loudspeaker for the helicopter itself, by going to iDroid > Mother Base > Development > Helicopter:

Since the SPEAKER development is an upgrade, denoted by the giant plus sign on the right side of its icon, you do not need to equip it explicitly. Once development is complete, the helicopter automatically has the loudspeaker built into it.

Now you can now assign music in the iDroid > Missions > Cassette Tapes screen:

Once you have the desired song highlighted, the button to press is Square (on the PS4) for Set Helicopter Music . Your platform will show the appropriate key bind at the bottom there.

I have heard that players on PC can import custom music of their own, but I haven't had any direct experience with that process myself.