stud chasing pregnant mare

Question
I HAVE A FOUR YEAR OLD STUD THAT HAS BEEN IN A PEN NOT FAR FROM MY MARE THAT SHOULD FOAL WITHIN A MONTH.  SHE IS ALSO PINNED UP NOT FAR FROM THE STUD.  THE STUD HAS JUMPED THE FENCE TWICE WHEN I HAVE LET THE MARE IN FOAL OUT (ONLY TWICE).  THERE ARE TWO OTHER MARES THAT ARE NOT PENNED UP THAT RUN WITH MY TWO GELDINGS.  THE TWO TIMES THAT THE STUD HAS GOTTEN OUT, HE HAS CHASED MY PREGANT MARE AND DOES NOT SEEM TO SHOW ANY INTEREST IN EITHER OF THE MARES.  WHAT COULD BE THE REASON FOR THIS?  APPRECIATE ANY ADVICE....

Answer
well i haven't had too many studs ,unless they were stabled at the race track in training to race ,  then i would always keep vicks up their nose , so they wouldn't be able to smell the mares in the stables. you might want to try vicking his nose and see if that helps.  thanks ED