Installing a BRP 1/2 cover is a bit of a pain. Spyder Sisters cover is certainly easier, but we have not purchased one as of yet.
I installed a Gorilla Alarm and just arm it as we walk away. Simple install and works well as a deterrent.
Agree, that if you approach someone on the machine, let them know you consider it that they were stealing it. Maybe start the cell phone video as you approach them. No different than climbing inside someones car or truck and sitting in the seat to "check it out".
Words spoken often are not a strong and powerful to prevent a next time. Other things mentioned in previous posts, certainly make a lasting impression.
There was another post long ago, I thought the Spyder owner went up to the person sitting on the machine and acted a bit as if they did not own the Spyder, then asked the stranger sitting on the Spyder what he drove. The guy pointed to his car and the Spyder owner went over and climbed in or sat on the hood. The guy was livid. He was then asked why he considered it ok to sit on the Spyder.