There are different kinds of "smart" and different ways to be "smart". A psychologist might say that you thinking someone is "smart", is because your IQ level is lower, so you WOULD think that person is smart, even though he/she really is not, etc.
IF DP has gotten away with more than one murder in the last 10 years, than IMO he was smart, or, every one else was dumb.
He might have done some smart manuverings with Stacy, (i.e. the killing, the hiding of the body, etc.) but IMO, he also made some mistakes. The reason that DP is where he is right now, is because of Cassandra and the exhumation of Kathleen's body. Had neither of those events happened, DP could very well have been adding another murder on to another year and gotten away with it.
What is frustrating all of us, is not knowing how many "red herrings" DP has put out there to LE and all others that are so involved in this case. It is a very time consuming process to eliminate those "red herrings" that DP did put out.
Is that smart? Absolutely! (In a LE's/criminal's mind)
Sorry, I feel like I've been gone forever!! Gotta catch up!