1 out of 100 for year 1
1 out of 100 for year 2
that makes 2 out of 200
which is still 99%
I believe the stat is also actually 99.9, or at least less than 1 percent...
Not only that, but you have to factor in what points in your cycle that you can become pregnant, and apply the statistic to that...
I'd say your chances are pretty low, but if you are still paranoid, a vasectomy is easily reversible for your fiancee.