How to delete one row from a mysql table 'completely' ?

Hello, everyone, if I delete one row from a mysql table, I hope nobody can recover this row at any time. I think the only way is to rewrite the correspond physical unit with other information. Now my question is: how can I find out the start address and the real length of this row in physical memory, and how can I write a same long record to cover it?
Any proposals are warmly welcomed! And thanks in advance!