Guarding units

I brought this up once before somewhere before but I've had more time to think about it. I always end up in a situation where all the troops designated as a guardian are at the edge of his allowed movement unable to reach his target but getting killed by range units.

For instance if I want to guard a tower, it actually works better to put units there with the defensive attitude. Once he has reached the allowed distance, he turns around and goes back.

But in the case of guarding say the hero, you have to set them to guardian or obviously they won't follow you around. I may be thinking outside of the what is actually possible, but is there a way to make guardians act more like defenders in this situation?