My Doxie boy is obsessed with squirrels!?

I often take walks with my mini doxie, and occasionally let him off-leash when on the back quiet country roads. But if he catches site of anything small and furry, he's gone. Is there any method that I can use to keep him nearby even when tempted to run after something? I know most of you will only tell me to keep the leash on him, but I enjoy trusting my dog and letting him wander in front or to the side of me without being completely restrained.My Doxie boy is obsessed with squirrels!?
Nothing that I can think of. That's what they were bred to do, chase and kill small animals. You could try teaching a really solid ';come'; command, but his instinct will probably be greater then training. You could try posting this in the dog section, you may get some more responses.