Hopper Protection

The issue of request-and-run hopping is very common.

My idea is to have troops donated by a clan to 'disappear' when that player leaves that clan, perhaps with the elixir cost of the troops being returned to the donor. I don't see many problems with this idea since a non-hopper who wants to change their clan will probably not care about the troops. This will 'destroy' the incentive to hop (apart from hopping, attacking and leaving).

What do you think of this idea? Is it good?

then they would simply join-request-attack-then leave using all the troops donated