According to one site I visited:
Animal scratches and bites, and other wounds contaminated by both human and animal feces and saliva, are potential breeding grounds for tetanus bacteria.

Children older than 7 years should receive tetanus toxoid as part of the tetanus and diphtheria toxoids (Td) for adult use, both for the primary series and for booster doses every 10 years.

I tripped and fell trail running yesterday and had to get stitches around my eye- the nurse in ER said I had a certain amount of time to get a tetanus shot if I thought I needed it. My husband thinks I probably should- how long do I have after the fall to go get it??
(My body is a bit beat up today and doesn't feel like going out of house.)

You should get the shot the same day as the injury, if possible. But, if not, you should be ok as long as you get the shot within 1-3 days after the injury.