To be on your tod means to be alone. If you're British, the chances are you knew that – but did you know the phrase originated as Cockney rhyming slang? The Tod in question was a jockey called Tod Sloan. Whether he was most often alone at the front or the back of the field, I can't tell you.
Alternatives are on your pat (Pat Malone) and on your Jack (Jack Jones). Who Pat and Jack were is something else I can't tell you. Maybe that's something you can tell me?