This is an old trick borrowed from drag racing. If you get superior traction (from a 'slick) many times you will spin the tire on it's bead around the wheel. A cheap fix is to drill the perimeter of your rim & use sheetmetal screws thu it into the tire to hold it in place. I've done it & it works fine, but when I drove my car on the street, the screws would eventually wallow & try to tear the tire bead.
No imagine this scenario on an off-road vehicle where the wheels encounter a LOT more stress/flex than on the street. I believe the screws might help hold the bead on, but at the cost of eventually ruining the tire.
I would recommend using a narrow steel rim (if you aren't already) and I've heard that the bead can be glued to the rim w/ contact adhesive to help more if everything is very clean. Personally, I've run 32x11.50.15 TSL/SX's on 8" steel wheels with approx. 5 psi & haven't lost a bead. If you have soft, pliable tires, they will unseat easier, too-- the Super Swampers are pretty stiff.