JRT keeps charging our Fish Tank

We recently aquired a 3yo JRT who has been a wonderful addition to our family. "Tugger" has been trained well by the previous owners. We have a salt water aquarium that was in the house prior to us getting Tugger. After reviewing posts here and others around the Net we are fully aware of this breed in regards to their needing to hunt. Tugger enjoys sitting in front of the fish tank and watching the fish move about. Our problems comes about when he begins to charge the fish tank nipping and licking the glass. With the way our aquarium is set-up I'm concerned that one day we will come home to a messy home with some dead fish, tons of water damage and a very hurt dog. Is there any advice someone can give us to help us out with this matter? We have had Tugger for about 4 weeks now and yes, he has seemed to calm down a bit with the charging but still needs to be told to get down which he does when we order him to.