Swimming is an excellent idea, it will help him lose weight and help his arthritis.
All I can think to do is cut out treats, feed a little less and keep him moving.
Sinister "The Prince of Darkness" 4 yr old black male GSD 3.11.09
Draco "Dakota's Unbreakable Vow" 5.5 mth old male Dalmatian 6.30.13
Cats: Chaos, Mayhem, Monster, Wicked