This game borrows so much from dota but seems to have left this out. For those that are plebs, backdoor protection is where if you have no minions near the inhibitor or the nexus it gets a lot of armor and regen making it way harder for just 1 person to win the game by walking through the jungle with no minions nearby.
[zombie-nunu-tears]
There used to be a summoner spell called "Fortify" back in season 1, but nobody took it so it was removed from the game. It made your towers immune to damage (all of them) for a short period when activated. This was especially useful back when Master Yi got flat AD from his E, and would eat towers for breakfast. Also, Twisted Fate's Gate was global.
Towers doing increased damage against a single target was made partly to combat this. Same with the inner towers having lazers, so that you take much more damage over time. I suppose they don't have the backdoor protection completely to keep it in as a legitimate strategy. Letting yourself get backdoored to a loss generally means you have bad map awareness.
Duct tape
Or maybe just ward your jungle and keep an eye on your base if your nexus is wide open?
