I believe as long as you have a corpie to keep feeding you figs, you would always be able to destroy the dock no matter how strong it is. The thing is in most games people don't have that kind of resources. But if they did. Example, in a recent game I was in the opposing corp blew it. I know they could have done it over and over again as they had billions of credits to buy figs with and had no problems making more money because they had the entire game on lockdown. Especially if the dock does in fact have a maximum defense rating and does not just keep going up and up.

corpies feeding you figs while you are attacking, never even thought of that. ick
Slim

There reaches a point where the damage SD will do when it attacks back is greater than your ship can withstand. It depends on the ship settings as to when that happens.