All of the above are great ideas, although I would agree with the able bobbing etc, probably best to only do this when there is someone on the yard.

I share your problems with the Likits, the last chap I had used to polish of a likit in less than a day normally, just bit straight in to it and ate it in chunks, which wasn't ideal, and not too good for them! So again, in agreement with the swede, apples etc hanging from the stable bars etc, although make sure you use something thick enough (we used old lead ropes) that won't snap and risk them either eating any of the twine etc by accident or end up getting it wrapped around legs etc!

The Likit Tongue Twister is great too, and usually prevents horses biting it all straight away!!

And I'm sure you already are, but small hole haynets/haylege nets are generally better as it takes the horses longer to eat them. Roma Horse Play balls are quite good too

Ideally though, nothing beats getting them out of the box (obviously weather permitting, I know last year with all the snow and ice it just wasn't even safe to get them out of their box) even if its just to lunge 20 mins in the morning, school in the evening etc etc (assuming you have floodlights in your school), and then grooming and interation when you can

Ah the joys of winter!!