Yikes
Little people and reef tanks do not mix well.
100mph tape and plastic twist ties would be first choice next to a barbed wire fence.
Just a matter of time before one of those little monsters will decide the fish look hungry.
Any coin today contains some copper or brass that will eventually leach into your tank resulting in the disaster you are describing.
Any child entering house should be clearly told about the angry crab in tank that will jump out and bite the finger off anyone approaching it too closely...
