The thing with prairie dogs is that they are a huge pain in the butt for both ranchers and farmers so what i would suggest is just simply take a day and drive around asking ranchers and farmers for permission cause more then likely they will let you and sometimes they will even pay per gopher you shoot.

Now as for tactics if you dont have a gun that is very good at long ranges(100+yrds) what you do is just sit down and wait then they will tend to start poppin up and just pick a few off them move to another spot and do the same thing. Then go back to the spots you have shot a few and the live ones will usually tend to be eating the dead ones and well shoot away.

If you got a good long range weapon well its pretty simple spot where there are a bunch of gophers, set up 100yds or so away and just start shooting cause they dont get as spooked if you are further away. Hope this info helps and welcome to the board.