A few things I have heard but have not tried. Before planting, check with a nursery about a barrier you can pound into the ground. Goes about 8-10" down. This keeps most gophers, moles, etc. from traveling as they only live 6" below ground. This won't stop them from getting out of the ground and traveling though. The other thing I have always wanted to try is galvanized metal cloth. It look like a big metal screen. Lay this down before you lay the sod. Make sure you get it with opening small enough to keep the critters from squeezing through. This will keep them from coming up or down through the yard. Should be able to get it from home Depot, Lowes, McMaster-Carr (
www.mcmaster.com) look for wire cloth.
Hope that helps.