Sounds like the walky dog would suit, my advice would be to fit it to the seatpost, at least you can sacrifice that if your dog proves as 'enthusiastic' as our last one was, lengthen the para-cord lead part if required. We've had our walky dog for over 10 years now, the last dog loved it, it got to the point I couldn't get the mountain bike out without him going nuts and he'd cheerfully run for 30 miles on it, he was a collie cross.