Ive been looking for a locking clip or something to put on the edge of the shelves to lock the tubs in place.

Well ive come across a solution! I know its not mind boggling, but it works great! In walmarts small electrical wire section they have plastic staples with nails in them.

If you take one side's nail out and then hammer the other side into the egde of the shelf you get a little knob you can turn that acts as a stopper for the tubs and it prevents them from sliding out. It also works great as a kiddy proofing mechanism.

Ill take a quick pic later tonight to show what I did...