Effective Range of 12 gauge shotgun shell?

I just read a post on this subject which helped a bit. However, I want to fine tune the question. I have a deer problem, getting worse every year due to new neighborhoods developing around my property, and I need to get some control. Plants that were never touched in the past are now being grazed down to their nubs. My question is, what is the distance I need to be AWAY from an adult animal, shooting at its backside, and be somewhat ured of a non-lethal or serious damaging shot? Using 12 gauge - Heavy Dove shells.