Not sure why everyone is attempting to DP links in the rucks when you potetially have Smith sitting as your 3rd ruck. I think he will provide more than adequate cover on those bye rounds or the one or two week injuries.
Anything longer than that may actually just require a trade, so not sure I am going to waste a spot in my forwards just for something that may never happen. I would prefer the DP links to my mids and forwards or mids and backs.
Smith if he gets games should be great cover. If Petrie puts up good numbers and you can play him as a forward with a DP link in the rucks, he can cover injuries rather than having to play Smith if the forward cover is better. All theoretical though.