FYI ... a squat pot is a 7 gal nursery can that is almost as wide as it is tall. Since they are shorter in height than the 15 gal cans, it is easier to use when you are burying a container for gopher control.
Roses don't have a tap root, just a few anchor roots and their root mass spreads out. So, no matter what size container you decided to use, be sure to drill holes in the sides of the container for the roots to spread.
@Dave ... thanks for the link for that trap. It looks like it would work very well if you were only after a few gophers instead of a whole colony of the beasts invading your garden.
Smiles,
Lyn