Do you happen to have any books on hand that deal with setting boundaries. I never really developed this skill, but it seems really useful and I'm in a situatio

Do you happen to have any books on hand that deal with setting boundaries. I never really developed this skill, but it seems really useful and I'm in a situation where I need it. My boundaries are clearly being crossed, but I don't know how consequences should be brought up, or how to actually go through with the consequences (I seem to cave pretty easily.)