During the 60s or 70s a groupe of Palestinian terrorists dived from Acaba to Eilat, and put a bomb in Eilat's water reservouir. They managed to blow it up, and hold the regular water suply for the city for a couple of days. Now there are navy boats patroling the area, and anyone who dives at night must notify the navy. There a couple more attempts, but all where stoped. There where also a few trys at the north (in variouse ways beside SCUBA- from a jetsky to fishing boats), again most where stoped by the navy, accept one case where terrorists in rubber boats came from lebanon to a beach at the north, and killed a few people there, took others as hostages.
There is no way to completly shut yourself from terror, I just guess, that for americans, to have a terror attack on your own land is a new experiance. Unfortunatly, here in Israel we got used to it. As a matter of fact- just a few days ago, by sheer luck a terrorist action in a gasoline and gas tanks farm was averted. If it had succeeded the results could have been the same as a small atom bomb (killing zone of about 800 meter radius) killing thousands of people.