Thanks everyone. I'm very worried about the potential for them breeding, it's not that I don't want to keep an eye on them, I'm just unsure what to look out for and how good a job I could do of caring for them both at that time. The breeder has not been keen for neutering as they feel it is unfair to put the pup through an unnecessary operation. However, I know they care greatly about the health of the Basenji breed and would be against any illegitimate pups being born.
The fact that one of his testicles is smaller than the other - is anyone aware of that causing heath problems for the dog later on in life? The vet doesn't seem to think so but still believes that neutering rules out a great deal of potential problems.