So you are saying you have a quick release skewer for your seat post bolt? Why? Get rid of it and put a binder bolt in there. It's cheap and super easy. And then if you are still worried about your seat post being taken apart and your seat being stolen then get a little cable to fish through the seat rails and your U lock.
But heres the thing. If a thief is taking the time and has the opportunity and the tools to wrench on your bike, you are gonna lose some stuff no matter what you do.

As far as seats go: Why does anyone have a quick release for their seat posts? Why do they even put them on adult size bikes? How often are you supposed to change your seat height? Never. That's how often. Set it right, tighten it, forget it.