30 inches deep wasn't enough to keep them out of a garden I put in here in California, but I would think that it really depends on the nature of your soils and underlying rock/hardpan conditions. This was a clay loam soil with no underlying impediment to the gophers going as deep as they wanted...

I quit digging at 5 feet once. It looked as if the hole was at least several feet deeper.

thank you for letting me know your experience. i was hoping that 4' hardware cloth would do it. making rootball baskets and allowing the gophers to eat what roots they can get at is not what i wanted for the best trees possible. i donbt like to kill either. maybe trap and relocate will do the job.

A nesting pair of barn owls are supposed to eat up to 1200 rodents in a single season. Try putting up a nesting box - owl size. I make aviary wire baskets for everything I plant and for raised beds I line the bottom of the bed with the wire. The gophers probably eat some of the roots that go beyond the wire but at least they don't kill the whole plant and the wire baskets give the plants a chance to get established.

Gophers can dig at least six feet down and that is usually where their nest is.

Linda