Hi, I know there have been posts about the Gentle Leader head halti, but I haven't seen anything on the halter. Has anyone used it before? If so, is it effective? I'd like to switch Boss from a head halti to a harness, he's been pulling to get at squirrels and birds *a lot* more lately, and I'm a little concerned about what some people have said about it causing spinal injuries. Any help would be appreciated. Thanks!