Motor Mouth (Alex Barnaby Series #2) by Janet Evanovich (2007) First Edition.

Barney is a woman with a taste for speed, talent for breaking rules, and knows too much about cheating. First there was boyfriend NASCAR racer Hooker and a salesclerk. Now an unlikely winner has to be cheating. Another spotter calls for help, trapped. Their drooling St Bernard leaves his teeth marks in a corpse. They are on the run, suspected of murder.