This won't be relevant for most readers, but my answer would have to be the $20 Gentle Leader for my dog. She is an incurable leash-puller, to the extent that t

This won't be relevant for most readers, but my answer would have to be the $20 Gentle Leader for my dog. She is an incurable leash-puller, to the extent that the nerves in her face were damaged and her jaw was completely paralyzed for 6 weeks. Needless to say, our twice-daily walks were very stressful for me for over a year. After acclimating her to the Gentle Leader, the problem is entirely solved. The only downside is that passersby often mistake it for a muzzle and assume she's dangerous.