Another way around the problem is to have damage done to the contents when the container via magic. The assumption is that the violence of the fireball/etc. damaged one or more items, damaging or destroying them. I've played several other games that handled it that way. Then you have the choice of lock-picking (if you've got the skill), bashing with a weapon (and the weapon takes damage), or using a combat spell (and the items you're trying to get might be damaged or destroyed).
