Frog Jars are a neccessity among all witches, wizards and mages.
What appears to be a frog is actually a very powerful summoned ward that is cast to protect the contents within the jar it guards.
The jar becomes a part of the frog's body and it grows increasingly larger to accomodate more items.
Frog Jars are surprisingly effective at protecting treasure due to the fact that they can only be dispelled by the one who cast it.
If a stranger attempts to steal it's treasure it becomes enraged and bounces around hysterically, and attacks mercilessly while bellowing at a tone loud enough to cause headaches.