Adding to Angela:
When I was in the military, I worked in a small hospital that did out-patient surgery, among other things.
When a man had a vasectomy, we instructed him to ejaculate 15 times,
to make sure all of his sperm left his body. After that, he should be sterile.
Sometimes guys are sore and will find it difficult to ejaculate 5 times in 90 days.
In reference to removing clamps:
Tell your doctor that you really want another child.
Sometimes the provice will pay for a "reversal" if the Ministry of Health can be convinced that it is in your best interest.