How to stopp nibbling before it turns into biting?

[dark_prince]

My 4 year old TB is very nibbly and always has to see what I am doing and always has something in his mouth.
Whenever he nibbles, it's mostly clothing but he likes to sort of suck on your hand, leadrope etc. When he does this, he sort of sticks his top lip out like when he's playing and pulls a face.
Anyway, I'd like some advice on how to 'nip it in the bud' before he gets too rough, and make him realise it's not playtime when we're out of the field!

 

[WestCoast]

I had to stop my mare nibbling at all times and not feed her treats except in a very few situations. I now say "personal space" and push her nose away firmly but gently, which she seems to understand. But that may not be a good idea with a sensitive, or head shy horse.

The problem is that if you let them do it in some situations, they don't understand why they can't always do it. She also had started nipping looking for treats.

Paula

 

[dark_prince]

I don't hand feed him anything, and tell him off whenever he starts nibbling but I don't think he understands! It's like he thinks I'm playing with him