To safely dismount Onewheel, always slow to a stop and then remove your foot from the rider detect area.
To remove your foot from the rider detect area, some good options include:
1. Heel-toe your foot toward the front of the Onewheel off of the rider detect area.
2. Go on your tip-toe, lifting your heel off the back half of the footpad.
3. Jump off with both feet! Nothing wrong with this, but always remove both feet at the same time.