Urine pooling is not good, as I am sure you realise.
We would use a lavage while in early estrus with Lactated Ringer's Solution (2 days or so before breeding) - using enough until what is coming out is as clear as what is going in. Then Oxytocin every 6 hours up to 2 hours prior to breeding. Repeat the LRS lavage the day of breeding 1-2 hours before breeding. Breed 24-48 hours prior to ovulation (assuming good quality fresh or cooled semen - have to breed closer with frozen or poor quality semen). Back on oxytocin 4 hours after breeding, and every 6 hours until 3½ days post-ovulation. Lavage again with LRS 1 or 2 days post-ovulation (2 hours after and 4 hours before oxytocin). Then cross your fingers.
There are some problems with the protocol you suggest, not the least of which is that if you give Regumate, you will be lowering the uterine immune response and then introducing semen and a variety of pathogens, while closing the cervix (and therefore preventing drainage) - a sure-fire recipe for disaster!
A urethral extension surgery is probably your best bet.
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