Rolling benches are great shop creativity ideas. If doing this, and your inside setup allows it, place the grinder on the end of the bench so you are pushing down the long axis. This is far more stable. A little ingenuity cold even come up with a grinder base that swivels to allow turning from inside use position to outside use.
Several methods work.
The simplest one is to use locking wheels. The larger and heavier duty wheels you use, the better.
Another trick is to use rollers, and to cut two 4X4s about 6" longer than the bench width. Once rolled to where you want it, lift each end and slide one under the bench to completely raise the wheels off the ground when the bench is in use.
Another is to use a mobile tool base. They are more expensive, and for a size like 3'X8' may be downright costly.
Other inventive methods will all do the trick as long as at least the end with the grinder is sitting in firm contact with the driveway/ground when in use.
