You'd probably have a better chance of a meteor coming through your roof and taking you out while you sleep than actually getting tetanus. There are a whopping 30 cases a year in the US. The study below says there is no difference in the occurrence rate between those who never get boosters and those who do, so long as you got the full series as a kid. Considering the number of people that injury themselves with rusty metal and haven't been to the doctor since they were in elementary school, I'd say your safe.
Tet Anus
I was going to get a fresh TDAP a few years ago and the doctor said it wasn't necessary since I got 2-3 as a young adult in the military. If you cut yourself, I'd worry a whole lot more about another infection.