help with mating yorkies

Question
Hi,
I currently own 2 yorkies. The Male (TOBY) is 4 years, Female (CASSIE) is 2 years. We have owned them both as pets since they were puppies.
My (their) problem, is that they dont 'tie' on or 'stick' to each other when mating.
We tried unsuccesfully last year to mate them, and this year the same is happening again. She stands for him, he is very interested in 'humping' her, but theres no actual 'tieing on' together, hence no puppies.
Is there something im not trying? Im used to breeding boxers myself, and that seems to be alot easier than this breed. help much appreciated
sam x

Answer
Hi Sam. Have you have her checked out? Sometimes a female can have strictures inside of her vagina that won't let the male fully penatrate her, resulting in no tie. The only realy thing that you may be able to do in this case is to try A.I. This may be your last option. If she has strictures, then this may be your only option. You can also try to hold the two together after he ejaculates. It's not the same as a tie, but it can work. I'd still have her checked out to rule stricures, or any other problems, out. Good luck!