My family are looking into acquiring and raising a cocker pup.

My children are 9 and 11. Both me and my wife work at home as dentists. We live in the city, but have a walled garden 7 meters wide to 30 meters deep. In front of our house there's a big park, very suitable for walking a dog.
3 days a week, from 9 am till 12 and 2 pm till 5 pm, the dog will be alone.
I plan to put a fence in my garden to make a suitable area ( kennel ) where I can put the dog during those 3 days. ( the rest of the time he will be with us; he will sleep inside our house at night ) I just don't know how big I should make it. Obviously I will take the complete width. As for depth: I have a concrete terrace (7 by 4 meters) in the back of my garden (previous owner had a kennel there ). In front of that is my lawn. Should I just take the concrete part for the dog? ( Obviously not an inspiring place to be in. ) Or shall I add another 4 meters of my lawn to the concrete ? This way I double the surface to 7 by 8 meters with a tree and half of it gras. Do you think this is the best sollution? Pro's: bigger area, more interesting, gras to dig holes in. Cons: dirty dog, probably will inspire the dog to dig holes in the rest of our garden.
It's not practical to leave the dog in the complete garden, since we have a small pool and if het gets in there he will probably drown... I also have flowers and plants in the rest of the garden, and I guess the dog will want to 'change' the lay-out of those a bit

Please some comments and suggestions !