A few things to note...
- A TO-220 MOSFET is way overkill. A BC337 is ample for such.
- Remember a fast diode over the relay coil, or the active element will die screaming.
- The schematic you were pointed to (one of the late Tony VanRoon circuits, stolen from his site BTW), does have a (slow) diode in place, but the resistors at the gate are way too large (always scrutinize his circuits and correct accordingly, he was a really great guy, but unfortunately, several of his circuits are flawed and he didn't get enough time on earth to correct them all).