I applogized up front for the length of my question.
Has anyone tried using a treadmill to exercise their dogs? I have been thinking about getting a treadmill to help exercise myself and my dogs.
Unfortunately, walking my dogs is only a workout for me.

I have bad knees and can only go so fast (speed walking rate, but no jogging). I exercise Harley (lab/rott mix) in my long hallway by throwing a ball for her to fetch. She will run for hours if my arms don't fall off first. I am having a harder time exercising Merlin (rescue rottie), I have tried the fetch game with him, but he has no interest unless Harley is playing too and then he will just watch her run after the ball and when she gets most of the way back to me he takes the ball out of her mouth and brings it to me.
Merlin and Harley go to doggie daycare on seperate days, so they get a days worth of play each week, but I know that is not enough exercise to keep them healthy.
I have tried taking them to the dog park a few time, but I seem to pick the times when the 'unsupervised' dogs (owner in the car watching them be nobs) are there pushing the other dogs around.

We spend most of the time there fending off snarling and snapping dogs than having any fun. I know that dogs at play can seem like they are fighting, but these dogs are NOT playing nicely at all (hackles up, no play bows, etc).
I have also taken them to empty fields on a secure 100 foot rope, but all they do is sniff things and roll in even worse unseen things.

They love it, but it doesn't get them the exercise they need.
With winter hitting soon here in Wisconsin, my pace will be slowing some and I am at a loss on what else to try. I thought about hiring someone to run them, but the sidewalks are not well maintained (bumpy etc) and are often covered in snow or ice. I don't want anyone getting hurt either. I have been looking for someplace indoors to run them, but most places are not dog-friendly around here (been looking for someplace else to live for a year now).
Any suggestions would be greatly appreciated.