One got out yesterday while I was cleaning cages, well two actually it turns out. I lifted the lid off to check something and saw one little hopper pop off the wheel onto the floor which I cornered and caught immediately. But apparently his little friend also made a break for it and I missed it.
The dogs were freaking out all night and I couldn't figure out why, until I just found them frantically pawing under the wine rack. There was a scared little hopper cornered under it which I barely managed to save for the snapping Scottie jaws of death (the dumber one is still trying to find it). I now have newfound respect for both the ninja skills of hoppers and the tracking skills of my pups.