How do you stop a dog spraying?? (scent marking)?

He has a one year old (just) Jack Russell.
He has just started spraying outside and occasionally does it in the house.
I believe if you get them castrated they stop but at this present moment i do not want this done as i may wish to breed from him in the future!
Update: laine - did you not read what i said - i want to breed from him so why would i get him neutered?????
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