Personally I wouldn't use a shock collar - too much potential for turning the dog into a basketcase. Though my bias is to limit use of physical aversives to life-threatening situations. What I did was start with a long lead ( not a flexi! 20' cotton) on walks, while we worked on her recall in safe areas like a fenced school yard. As her recall improved, we'd let her drag the leash on hikes. If she got out of our comfort range, we'd say "too far!". If she returned right away, she'd get a treat, and get to continue walking as before; if not, we'd retrieve the leash, and she'd have to walk next to us for a while. After a while, she's get off leash for short intervals, then longer ones, always being put back on leash if she violated our agreed-upon distance, or if there were things about she looked likely to chase. It was a slow process, but now I can trust her around deer, cows, horses (though I can't trust the horses, so I leash her anyways), so I consider it worthwhile.