I am not aware of ANY device to stop a Motorhome from moving with the slides deployed. I have worked on thousands of motorhomes in 34 years and have never seen such a device. Now to the practical part of this question. As you found out, you looked in your SIDE mirrors and found the slide out. IMO, ANYBODY that would start a motorhome and put in gear and then move more than 5 feet WITHOUT noticing the rooms deployed in the side mirrors should NOT be driving a motorhome. They do not have the common safety sense to be driving, much less a motorhome. Doug