I asked the vet about shearing Mozart (a Newfie mix) some 10 years back, and he didn't think it was such a good idea. He explained that unlike humans, dogs don't perspire. They dissipate heat through their mouth and paws. Their skin is more sensitive to sunlight than ours is, simply because it doesn't get hydrated by sweat. He told me that heavily coated dogs (like Newfoundlands) will usually shed their undercoat when living in hot climes, but keep their topcoats to protect themselves against the sun.
Mozart was born in Florida
, and when I adopted him, he had no undercoat whatsoever. His topcoat looked more like human hair than anything else. When we moved to the Pyrenees for 6 years, his undercoat grew so thick that I had to buy him a bigger collar. We've been back in Florida for 3 years now, and the undercoat has totally disappeared again.
I think the best thing for a hot dog is to keep a kiddy pool with a couple of inches of water
in it at his/her disposal. Mozart hates water
(go figure), but loves to lay down in his pool (complete with Sunbrella) every half hour or so when he's outside in the Spring/Summer/Fall heat.