Rule G11 says you cannot detach, what about a string? You could still make a wall and still somehow score.

No, nothing can purposely detach

I believe if you’re still connected to your wall with something, then it is legal. It has been done in the past. (Tossup wall bots connected with only wires.)
Just as long as you never sever the connection.

But your not detaching if the string is attached

Even in Skyrise, we saw robots that sat in their starting position building skyrises or walling the middle of the field while a detachable bot scored cubes around the field. Detach I think is not the right word to describe it though, as it carries the connotation that the object will be fully severed from the robot, which most definitely is illegal. However, creating a multi-part bot as long as it abides by all the rules in its out state (of special mention is entanglement rules) is perfectly legal and can be a very strong strategy for creating a multi purpose robot (think both wallbot and catapult).