See if you can't buy a few Kingsnakes and let them loose in the yard. They'll drive out the rattlers (either by out-competing them for food or occasionally eating the damn rattlers). You might see if you can rent a propane gopher killer* and find all the snake holes first (they live in holes about 2" in diameter).
Then make sure you do what you can to keep rodents out of the yard as that's why the rattlers are there.
Also keep as much of the area around your house mowed as you can.
*I found these guys up in Loveland.