Get the biggest geo (altifrons I believe), which can get up to 12 inches in size. If your fish are smaller, it might have a chance. If you just want to make sure there are no pockets of sand, get malasian trumpet snails. Breed them first in a tank and dump them in.
Dont do any geos with your stock. Although they are great at digging, you create another set of problems with stocking. Just give your fish some time. Mine took about a week to realize there was sand where the gravel used to be, which really pissed off my Midas because it doesn't stack as nicely