Ric, I missed your post.
I like that gas idea. How soon would it lock the engine up? I ask because if it locked up quickly, they'd still be on the railway, fairly safe from high speed and injury. I wouldn't want someone to get hurt if there was potential for a car accident.
That's an interesting idea about pads for A/C units. Thanks, that's what I'm looking for - potential uses for these things and how they could be of value after all the labor to get them.
If I know what the slabs were used for, I stand a decent chance of finding out who stole them.