Pearlsacarolsinger
Up in the clouds
Agree you have to watch like a hawk...mine pulls to grass and I have tried everything to stop it. The only thing that works is being tuned in and stopping her as the first flicker of a grass though sparks across her brain. Once she has started to move it's a battle of strength which you will lose.
She is a clever one, she used to speed up to get a little slack in the rope then lunge for grass, I realised what she was doing so never allowed her to get that little head start....then she started briefly hanging back then diving for grass behind me. I swear it's a battle of wits!
The problem is that you can't really reward them for not pulling to grass, the biggest reward they could get (in my girl's eyes anyway) is a mouthful of grass. No reward you can give will trump that grass.
I have also tried firm and fair punishment but it makes no difference. It's like trying to work with a junkie, the grass hit it worth the punishment.
There are quite a lot of food rewards that most horses will choose over grass. Are really saying that if your horse is eating out in the field she will not raise her head if you offer carrot/polo/something else? IME when leading, most horses believe that a bird in the hand is worth 3 in the bush! (Substitute the word 'treat' for bird).