Haha, I followed you for your Lone Survivor game and you followed me back.
There is a trigger in the water to destroy bullets and tanks. However it is not infinite so you might get passed it. I now use a timer or max x/y coordinates in this type of situation but had not in this game. I might fix it.
The destruction effect is from a plugin from the Unity Asset store called Smart Slicer 2D by FunkyCode (I haven't got to adding the credits in the game description yet). Since then they made another plugin called Smart Destruction 2D which might be more appropriate.