No Shows on CLs

Every year we have a number of "no shows". If someone has booked and doesn't arrive our first reaction is that we hope nothing untoward has happened on route, but when nothing is heard it is annoying, causing us to have a vacant pitch for several days which could have been occupied by another member.

We do now take a deposit but this doesn't stop some people unbelievably.

I have heard from other CL owners that some members book sites at several different locations and decide by the weather which to go to.

Any suggestions how we stop this selfish behaviour?