I have no issue at all with breaching regulations, particularly modern ones, but it is a good idea to operate safely!
In the case of 'display' depth charges, one approach which is often taken is not to have small explosive depth-charges at all, but to fire dummies, and wire the pond with small underwater charges. These would be like little mortars, resting on the bottom, firing a jet of water upwards without any danger of cracking the pond base. Ignition is both safer and more reliable, which is what you need for a demo....