If they keep exploding, it suggests that they've been thawed and refrozen, that you may be warming them too fast, or that they've been stored too long. You may need to try a different source for your rodents, turn your freezer a little colder, or thaw overnight in the fridge and warm up more gradually. I've had it happen to me, but only a couple of times, and I definitely wouldn't want it to happen repeatedly, so I feel for you.