If you see multiple enemies coming bot for a gank...

Ditch the turret and run for base. 1 turret is worth less than 1 turret, two kills, 8 assists, dragon, and a whole ton of farm for the enemy ADC.

The best way to deny 5 man ganks bot is to make it an over-kill effort for just a turret. Hell, rotate mid or get vision on drag and your jungle so you can prepare to punish misposition if they invade.

It's not fun. But it's not impossible to punish. And the wave pushes, so your bot lane gets to farm up.