I don't recommend the lesser depth or
the use of a GFI to protect the entire run of wire as it will be more
subject to nuisance trips.

Why would it be subject to nuisance trips?

I was about to ask the same question.

I have all kinds of circuits (including exterior lighting -- my household
wiring is a hodgpodge) which I protected with GFCIs for "belt & suspenders"
purposes. An older ice box (1975? model occasionally popped a GFCI on
defrost and a dishwasher that had a leak likewise occasionally tripped a
GFCI.) Exterior lighting just hasn't tripped it either.

I have even left an extension cord plugged into a GFCI and after a rain
storm the cord is still hot. (Not every time, but yes, I tested the
GFCI.)

I not longer believe in nuisance trips. If a GFCI trips either the GFCI is
messed up or there is something really wrong that can and should be fixed.