I had to stop trying to heel Roxy for a 3 miles walk...wasn't gonna happen. I do some heel and some loose leash and alternate...I try to give her a hand or eye signal of what I want.
I found string cheese chopped up is GREAT motivation along with hot dogs * I use the turkey ones and in small bites and not many at one time*
Most of the time now when I walk I do loose leash unless we are being approached and then it's heel. I work on heel a lot in our fenced in play area at home