I aggree it is best if the dog is in the boat with you.

Our dog Innis wants...well HAS to be in front and HAS to be able to see everyone up close. He gets excited and stands up and jumps around if the other boat is too far away (over 10 feet, well, 11 :-) He has no desire to be in a boat by himself. Admittedly our pup has his issues. Most dogs are calmer but I'm sure the logic applies to most dogs.

I have built Two double kayaks and routinely bring Innis and my son in an open double. I plan a small tripple capable of a large and small human paddler and a large furry one or some other combination of large and small humans and dogs.

I should start on it as soon as I clear the workshop of the current project, a Hybrid 19 foot Baidarka.