Normal for a dog is 100-102.5. Depending on the underlying condition of the dog 103 might be grounds for panic. At 103.5 the dog will usually act very depressed. Likewise a temperature of 95-97 is critical as in organ failure and shutdown.

As for taking a temp- get a digital rectal thermometer. Lubricate it, and with a cooperative dog it's very easy to get an accurate reading. Label the thermometer as being for the dog!