My mini schnauzer has urinated on my leg!

I have an 8 month old mini schnauzer who has recently started lifting his leg and urinating on my leg/foot whilst in the park.
This only seems to happen when I am chatting to other dog walkers or petting their dogs. He does not appear to have any dominance issues, is very sociable and not at all possessive, with a very sweet nature.
The only other problem I have with him is running away when he sees other dogs, which I have been told is normal for his age.
He has not been nuetered. Any help?