Though someone could just move around on a single area without attempting any jumps... I think something should be done, but not sure if this'd work :p
I was going to make a thread but I'll add to this one to keep all the info together:
Following my "New Nether" thread, Liv (the island owner) and I found our previous Nether Portal. It was broken and the entire area was griefed.
When we do /is in the Nether and select the island options...