Tile – What’s the risk of water/rain falling on a recently placed tilework that’s not grouted yet

Absolutely. Those tiny tiles will chip or pop off as soon as somebody smacks it with something. I assume you are thinking of some nosing like this and where I live, I would certainly go with something with some grip.

Not knowing what kind of traffic the stairs get and what your climate is like (how often it freezes - how often they are wet), it's hard to make a more informed recommendation, but those thin small tiles will not take much abuse.

There are basically two types of wire tracer:

• audible frequency transmitter and receiver often used with telephone wires to detect them in floors, walls, etc. It is expected the receiver can be placed within a few inches of where the traced wire potentially is.
• low frequency RF (400–500 kHz) intended for detecting buried wires or inside structures where the receiver detector can be up to a few feet away.
• There are some which can do both audio and RF.

Each type has its tradeoffs. The RF system can be difficult because of how the trace signal propagates through conductive conduit or nearby wires (like grounds) so it often seems like the "wire" is everywhere. The audio detector often seem like the signal disappears and it is only by occasional blind luck that you find the wire.

In the case of a wire buried in a yard, I would think the best way is to dig up the wire. That way you can easily follow it and get a great feel for how its installation is aging, how well it is staying out of the way, etc.