Taking a break from Skyblock, I returned to find my neighbor Austin_H4, whom I've never seen on or has built anything, decided to build a nice dirt bridge right up to my island( yes I built a small part out of protection ) he destroyed a few things and everything is now in protection but maybe he should lose the privilege of having a island.

Now, I can understand the dirt bridge, but...

Did you by any chance have him added to your island's party?

People are only be able to build and destroy blocks on your island if you add them to your party. Unless you added him to your protection zone he shouldn't have been able to destroy anything.

You are still able to destroy things within others island with creepers. Not hard to do. Only way to prevent them 100% is to use /is lock. At least then the player will be unable to enter the protected area and limit the possible damage that can occur. I would recommend that you have at least 1 space between your island and the outer limit of the protection. They wont even be able to jump on if your island is locked this way.