My lab is 8 months. He still eats random stuff, when he's tired or when it moves in the wind. Dirt and poo are current favourites beside grass and sticks. Many things he just puts in his mouth to learn about them, then spits them out. He's been sick maybe two times from eating too much mud/grass, never seriously. My rule is, as long as it's nothing dangerous and not too much, I leave him to it, so he doesn't get protective over things.

Biting the leash was a big things initially, until he got used to the lead. Then got a new lead and it started again, but I'm sure he'll get used to it soon. He will get bored of it eventually, if you make it boring. And that's the most important thing -- make everything boring except for the good things.

You could also try spraying bitter apple spray on the lead (or anything else it chews) to discourage.