
I can't better what monkeyj has written. Please be very careful about who you allow the male to mate with - the owner of the stud dog is 50% responsible for what he produces, from what quality he produces, to the homes the puppies go to! It might be 'flattering' to be asked to use your dog, but fact is not every bitch will be 'right' for this dog, conformation/pedigree-wise. When we had a couple of males 'at public stud' I turned away more enquiries for them, than I accepted, simply because I didn't want my bloodlines mixed up with poorly bred lines. The income from studs was immaterial.
"18th old chihuahua. " What age?
ps If you do allow him to be used, you should draw up a Stud Agreement, stating the cost, and what free repeat matings you will allow. Ours said 2 puppies only does not constitute a litter and we offered a free repeat, once. We based this on the Contract the owner of the first outside stud dog we went to used. And yes, normally bitch to stud dog rather than him to her. Some people will board a bitch if they don't get an immediate mating to avoid people having to keep travelling.