You probably need to talk this over with your vet.
I have several friends who have kept neutered studs as pets and once they were snipped any spraying stopped.
My ex stud boy had never sprayed so it wasn't an issue.
They can have an injection of something called Tardak- but I believe the timing is crucial for it to be really effective.
As I say your vet would be best placed to advise you.
Good luck