Ripping your valve stem out is a terrible way to end your ride. Try this next tire change: when tightening the rim lock, (especially on a fresh new tire) make sure to re-tighten it after a bit of riding. The rim lock will "bite" into the tire slightly after a few stops and starts. Tightening about 80-90% followed by re-tightening will increase the "bite", more than one extreme torque job. Rims can be deformed quite badly from over tightening rim locks.
If very low psi/run-flat ability is desired, using two rim locks spaced 180 degrees (opposite each other) on the rim is the best option.
For extreme cases like competition hill climbs and sand drags, some racers will drill six or more holes through the rim flange and screw the tire bead to the flange with sheet metal screws. Usually this is only required with lots of HP and traction. Roost with confidence!