I don't force sharing so much as encourage turn taking. If someone wants a toy that someone else has, they can ask that person for it. That person in turn can either give it to them or if they aren't quite finished they can say that they'll give it to them when they are done.

What the OP is describing would not fly here though. If you aren't using a toy than anyone else can use it. I have one dck who started this a few weeks ago and I nipped that in the bud so quickly it wasn't funny.