Our normal clover clamp with an added chain to link them together
Clover clamps are designed to exert a moderate pressure from their rubber tipped jaws. However when they are pulled, the clamps are designed to tighten up in accordance to the amount of pulling force on them.
The added chain gives a good attachment point for weights as well as providing something to tug on! Most importantly, the chain avoids the frustration of only being able to find one of the clamps at that crucial moment.