There is a continual problem of disposing of unwanted cars. Some people dump them by the side of the road, others pay to have them removed. Why not get Excel to help out with the problem: If you have an old banger that needs to be dumped, let Excel have it to practice clamping.
Do make sure that you remove the number plates and tax disc so that it can't be traced. Better still, once on private ground, swap the number plates around to give them even more fun.
Just a handful of dumped cars in each of their car parks should get the message across.