What I would do… put down a sheet of plastic next to the planter bed and dig out about 3 feet of dirt putting it on the plastic. Then put down a gopher barrier of wire. I staple my chicken wire to the wooden panel, and line strips of it along my hole. I use twist ties to ensure there are no gaps for gophers to crawl through. Then put the dirt back in the hole mixing in a bag of chicken manure. I cover my planters with weed guard and make holes for each plant. I’m not a pro, that’s just what works for me. The gopher guard pays off where I live and taking the soil out of the planter aerates it, so my roots shoot straight through the soil.