So I was wondering, has anyone dealt with a horse that is totally territorial over their herd mate?
My friend has a gelding at the same barn I'm at, and he's in with another gelding.
She's about ready to give birth, and it makes her nervous going in to get her horse.

Her horse's name is Pongo, and the other is tug(so that way I wont confuse you!)
When she goes to get Pongo, tug starts coming at her and then herds Pongo away. Pongo usually just comes right up to her, but now with Tug pushing him away, shes too nervous to even get the halter on.

I'm already thinking on sort of pushing tug. If he comes up to herd pongo, I herd him away kind of thing.
We can't do much with Tug since he isn't ours, but safety has to be number one, no matter what.

Any ideas?

I would remove him from the same enclosure, sounds like he's getting aggresive and that's not what you want, pregnancy or not.

I unfortunately deal with this issue constantly. -_- My horse is in a field with five other geldings, and he's definitely the lowest ranking herdmate so they like to push him around. Most of the time they will leave me alone, but occasionally they get too excited/sassy and try to chase Indy when I've already caught him. I usually have to catch Indy with a lead rope and use his halter to sort-of scatter the others. I just swing it at their shoulders (without making contact) and they get the message.. Usually :') Even though they make me nervous, they don't SCARE me because I know they're just being goofy and need a reminder to act properly. The "alpha" gelding has actually started helping me with this recently.. He lets me catch Indy and then herds all the others away from the gate. It's kind-of weird but I'm not complaining!

Your situation is harder though, since it's just the two of them.. and any horse coming at you in an aggressive way like that is not OK, like Sam said. Is there anyone you can bring this up with, like Tug's owner or the owner of the barn? It doesn't sound safe. :{

We had to get rid of a gelding (like, he was sold to a lady who kept him in a field alone, not anything sinister haha) who decided to start attacking people who tried to take herdmates out of his field if it was just the two of them. Sometimes he could be distracted with grain in a bucket (placed far away from the gate), but that stopped working eventually and there were several occasions where I couldn't get my own horse out of the field @_@

I would seperate them as well....

I like my animals being in seperate pens anyways, but i dont board either...

We are trying to avoid seperating them, because it would suck for them to be alone (they have been together since Pongo arrived)

I watched her landlord catch horse (they co-own) and he tried a little bit but nothing what my friend said. I dont know if its her own fear or what, but im thinking that Tug might just know shes a hit of a push over?

Is the pen big enough to split in half?!

I had my horses together and one was getting fatter so i just hotwired it in half....

I think horses absolutely know who tey can and can't push around, but when they act on it is when they are dangerous. Pregnant women, children, elderly, or just scared adults can be very, very bad if a horse goes after them.

RESPECT!

Tug is disrespecting the owner of the other horse.  Regardless of circumstance, horses are herd animals.  Tug is showing disrespect tot he owner of Pongo by moving Pongo away.  By getting nervous, the owner is reinforcing Tug's notion that he is the boss and that she is nothing but a low rung on the ladder.

At the breeding farm we went through this with a LOT of horses and it boils down to the fact that Tug is being disrespectful.  I suggest contacting his owner and discussing this.  Is Tug like this with his owner?  Is it possible to have a working session to earn some respect?  Liberty work does wonders to earn a horses respect and the owner might allow it.

In the end, its her choice, but all it might take is a firm attitude and a firm "NO" to Tug.  I'm not saying abuse him, but carrying a whip and making it clear that you won't be bossed around does wonders with attitude problems.  Cole used to be highly agressive but one glimpse of the whip and he would act an angel.