Kiel - Depends on what you mean by a release form. If you are saying you'd like folks to sign off on liability regarding trapping equipment in the likelihood that someone or their dog should get into a gopher trap, that would take some legal writing and even then might not fully protect you with visiting a lawyer and spending a few bucks and hours on getting something that fits NM.
If you are talking about a contract to be sure they pay you (not what I think you mean, but just in case) many folks offer up their contracts on here, mostly through PM to folks starting out.
I'm North of you, don't use a form for p. gophers, but understand your concern. Feel free to PM me if you want to discuss more local aspects, otherwise I'm sure others will chime in with some good sound info.
Liability is a concern for anyone that wants to be around 10, 20 or 30 years from now and should be everyones concern. However there are many things that can happen that folks don't anticipate, some of that is covered by insurance, others maybe not.
Can you illuminate what you concerns are a bit more? Are you worried about folks messing with equipment and getting caught, or dogs digging up traps, etc...?
Most of my gopher clients are residential, versus rural ag as you have been doing.
Justin