I will let you decide the parameters of the conflict:

You already said you do not grow in protection, would you like to fight right oop? Or would you like to grow to 1500 acres and fight or something? If you are growing out of protection to reach a goal, then there should be no restriction on protection growth.

Personally, I prefer we set an acre goal, first player to reach it must wait for the other and then once both are ready the fight can start.