Safe teleportation - pools

The lethality of the Teleportation spell can be brought down to 1% if the mage is very familiar with a pool of water at least 20' wide and 10' deep under an open sky or ceiling higher than 10'. A powerful wizards home would likely contain such a pool with a permanent illusion at the center as a point to aim at. In case of an emergency travel to any place could be safer if the spell is aimed just off the coast or in a lake.

An off-target result when castingTeleportation drops you 1d10 times ten feet from your intended destination, which is to say, up to 100 feet in the air or up to 100 feet away horizontally. That 20-foot wide pool is only going to catch you about 10% of the time unless you extend it to 200 feet wide, and the fall might still kill you if you appear high enough above it - and it'd need to be at least 100 feet deep to eliminate the possibility of your arriving in solid matter underneath.

Having a 200 foot diameter hemispherical outdoor pool adjacent to your bedroom is pretty sweet, but might not be considered worth it by all ninth-level mages.

Maybe that is why wizards like to put their towers in the middle of large lakes :P