Can someone clarify that this punctuation is fine?

I just wanted to check that the sentence below doesn't contain comma splices, as I am still not entirely clear on the subject.

He got to work digging up the weeds in the front garden, the same way he tackled them in the back garden, except these ones were much tougher.

(Sorry for the poor example; it was the only one I could quickly think of to illustrate my point.)

It's my understanding that this sentence follows the structure independent, dependent, dependent—is that correct?

The one I am most in debate about is the middle clause, as to whether it's dependent or not. I don't think it can stand on its own, but I'm not sure.