Gelding + Mounting + mare = HELP!

My gelding was gelded ASAP he is almost two and is already gelded. He is almost a bit bigger than 15 hands and my mare is only 12.1. Our mare is in heat and I was wondering if we should seperate them or what because he keeps mounting her! we tried to stop him, but it didn't work so we stalled him for awhile, but we can't keep doing that. I am worried he will hurt her. She leads him on, but then kind of grunts when he mounts her so I cannot tell if she is in pain or not? Please help any suggestions are appreciated.

When he was gelded was it possible that he has a testicle that didn't drop? I've also heard something like the more they take out ... the more calm the horse is. If the shorter the cord they cut, the more 'stallion stud' they act... but I don't know if that is true or not.

How long has he been gelded for? Do you know for sure if the vet got both testes entirely?
I would separate them for the time being; last thing you need is an injured or pregnant mare.

I agree with JDI. Separate them for now and you might have the vet come out and test his testosterone levels. They may be high or he may be "proud cut". I wouldn't really worry about him hurting her just by mounting her. If she is healthy then the weight shouldn't hurt her but the risk of either one of them getting kicked and injured runs pretty high.

What's already been said about double cheaking that he has been properly gelded is sound advice.

If you are certain this is not the issue there are supplements you can give to help with that kind of behavior. For example something like this which is ment for mares but works for geldings too.

If he's not a crypt, and it's been a while (better than 6 weeks) since he was gelded - don't worry about it. If it was perilous to her, she wouldn't ask him.

I wouldn't worry about it. Maybe get him checked to make sure he isn't proud cut or anything.

My gelding, Loki, mounted a mare in heat once that I know of and probably more than that. She kept bugging him and leading him on -rollseyes-

He likes to think he's a stud is all. He's gelded properly, but has always acted 'studly' since he was a colt. He's just a show off really :p

I wouldnt be to concerned I have a proud cut gelding myself he gets alittle studdish and has his mares but usually the mares put him in his place if you are extremely concerned have him looked at again to eas your mind but its really hard to break even at 27 lightning still mounts mares once in awhile darn horses and the most recent is 14 hands so and they are both ok

haha your basically describing my horses :P plus you made me laugh hehe

Thanks everybody you all helped a lot :)