Cedar used to act that way when the lead was on her collar. Like you, we didnt take the time to put the harness on her each and every time she needed to go out. We still dont. But we were insistant on using the lead. It meant we had to use the lead more, not less. And if she chewed and started messing with her lead, we had to use commands like "drop it" and "watch me" to get her to stop her behavior and give her attention to me.
If the lead problem is really bad, you can put something like bitter apple on the lead, so it tastes bad. If you're currently using a leather leash, change to a nylon one; they apparently have less chew-appeal than the leather. (Not that the nylon isnt chewable....)
I know there are a lot of opinions about using leads on collars with Cavs. Most of the time, we use a harness. But the quick outings to the backyard without a harness are still leash on collar. Just be careful not to jerk or pull on the lead too much. Commands that get the dogs attention so the dog drops the leash on its own worked the best for us.
Dont you just love puppies?
Cedar (tri), Willow (blen), Holly (ruby), & Bella (blen)