"Tetanus is caused by bacteria (germs) that get into your body through a wound, such as a cut while gardening, or an animal bite. You are more at risk of developing tetanus if the wound is deep or if it gets dirty with soil or manure, but even small wounds such as a prick from a thorn can allow enough bacteria to get into your body to cause tetanus."
Never mind gardening, how often do you get back from a run with a cut with muck in it?

Out of interest I checked when I had last had a tetanus jab; now I'm booked in for one as it was over 10 years ago. I think this will be the last one I need
as after 5 you are protected:

"As an adult, if you are not sure whether or not you have been fully immunised (you have not had the full five doses), see your GP or practice nurse. They will be able to advise you about having a 'catch up' injection."
http://www.cks.nhs.uk/patient_inform...eaflet/tetanus

It is unlikely that anyone will remind you to get vaccinated (no governemnt targets!), so it is worth checking if you can't remember when you were last done.