How do I stop dogs from urinating or pooping on my sidewalk. People walk their dogs and let them go anyplace. I have spoken to a few people when I see this happening and they all say the same thing - I can't help where the dog goes, he goes where he wants. My reply is always the said, "How come your dogs never pees or poops on your property by always someone elses."
I have tried Repel All but it does not seem to work on either the concrete or grass.
Is there anything out there that I can use to stop this problem.

When you say your sidewalk are you referring to Town/City property in front of your house, the right of way, or your actual property?

If it's actually your property I would stop people after you see this behavior and tell them you find it unsanitary and unsavory. Then I would check with your Town or City to see what the laws are.

Gosh, I die of embarrassment if mine happen to need to poop when I am out walking them. I always carry a few plastic bags to clean it up.
The urination is unfortunately hard to stop especially with males but the pooping should be cleaned up as soon as it's done by the owners.

It is my property. However, where I live I'm responsible to maintain the city property in from of my house. There is a fine for not picking up poop. It is only inforced if it is witness by a patrolman.

I have a neighbor that collects the poop in her yard and deposits it back in the offenders yard. :D