I am assuming you are "true light photography" as I plugged in your name and that is what came up.

At the dog park, you are dealing with strangers who may be a bit leery of someone handing out cards. Then, to get them to buy something they were not looking for, it has to be a photo that they themselves could not capture. In the world of cheap DSLR's, that is becoming harder and harder to do

As far as the portrait sittings, again, make them so good people want large versions of them. Make them look so nice that people invision hanging them framed large on the wall.

Target your market and find what it is they want and want to buy. The dog park thought is a good one, I just don't think it will result in many sales.