Take temperature orally?

My dog is recovering from pretty serious surgery. I am supposed to be taking his temperature on a daily basis. This is much easier said than done given that he is a large dog with an almost non-existent tail that he can clamp shut at will. If I had to, I could have a couple of folks sit on him (like they do at the vet) but it seems like taking an oral temperature would be equally effective. I have been told by a vet that the touch/read thermometers are not that accurate on dogs. So, I am using a soft-tip digital thermometer that measures the temp in 10 seconds. My dog is very used to having his teeth brushed and tolerates the thermometer in his mouth with no inclination to bite it. I am just laying it along this inside gum/cheek pouch towards the back. As long as I make sure he hasn't been eating or drinking anything in the past 20 minutes, I am wondering if this is an accurate reading. The only explanation I could find for not taking oral temps from dogs is the fear that they may bite a glass thermometer and ingest either glass or mercury. That is not an issue in this case. He seems to be doing well and shows no outward signs of fever. I don't want to stress him out and risk him popping staples if I don't really need to. Can you tell me if taking his temp this way (temp is a little over a 100 degrees) is ok? Thanks for any advice.

I will do this a few more times to make sure it is consistent but it does seem that there will be an approximate one degree difference. The oral temperature is about that much lower and I have done this twice. Of course, it is warm here so the dog is panting. Luckily, the anti-seizure meds have kicked in so he was pretty relaxed for the whole thing. Regardless, it is somewhere between 100 and 102 so I am happy about that. Thanks so much for your help.