It may well be that your pup has a preference for the wet food, and there's no reason why you can't continue to feed canned products if it works for him and you.
It may also be that there are ingredients in that food that don't agree with him, and he's signalling that something else might be better.
Although Purina has a lot of products out there, it's really not a very nutritionally good food and there are many ingredients in it (corn is a biggie) that many dogs don't digest very well..I'd still check out the food forum for some tips and suggestions.
On the free feeding, there a few things you might want to consider: Monitoring your pets' daily food intake is really important for a few reasons. First, you can adjust the daily amount you feed as needed if your pet is gaining/losing weight - you should routinely monitor your pup's body condition and adjust the food as needed. Free feeding, where they can "nibble" all day, is often a huge contributor to obesity, which is of course not healthy. Measuring your pets' food can also be a helpful indicator of illness...if you know your pet always eats half a cup of food in the morning, and one day only eats half that or turns his nose up at it completely, or conversely starts begging for more food, you might be getting an early warning signal of an illness.
Solomon - black DSH - king of kitchen raids (11)
Gracie - Mutterooski X - scary smart (9)
Jaida - GSD - tripod trainwreck and gentle soul (4)
Heidi - mugsly Boston Terrier X - she is in BIG trouble!!! (3)
Audrey - torbie - sweet as pie (11 months)
Patrick - blue - a little turd (but we like him anyways) (6 months)
Boo, our Matriarch (August 1 1992 - March 29 2011)