You say they are together 24/7. If she is ready and ovulating she will be more aggressive about her intentions to him like you are seeing wth her mounting him. I would try having part of the day when the are apart to...absence makes the heart grow fonder most of the times in dogs. Good for him to be able to smell her and not have access to her for a while. You'll probably see his drive go way up
. What I would now like to know is are there any signs I should look for to tell if she is prego besides that? 