Well, that didn't take long. I just found a small bug in the way I did it.
Say I have a discount code that's set for 10% 1 specific product. If I don't have that product in my cart when I use that code it tells me the code isn't valid for my current cart like I want it to. If I do have that item in the cart then the code works fine and calculates against only that line item, which is wanted.
However, if I remove the item that belonged to the discount code after the discount has already been applied it's leaving the discount on the order.
So now I'm stumped again. I hadn't seen your response until already went down the other road so I'll look back and maybe try that route.