Drop minefix.smx into addons/sourcemod/plugins and minefix.games.txt into addons/sourcemod/gamedata. Requires SourceMod 1.6 or later.
By default it will simply passively block the exploit by triggering rockets to explode when they come into contact with a sandman ball. If you have SourceIRC, the plugin will announce attempts to use the exploit to your "ticket" channel. It can also be configured to automatically ban players who fire rockets that touch sandman balls. While this is rather difficult to do by accident, it is possible, so it's recommended that you require something like 3 or 5 detections before you start banning people.
If you want to ban people, here are the appropriate cvars:
minefix_ban_detections - Number of times a client has to be detected trying to exploit the mine glitch before being banned, or 0 to never ban (default 0)
minefix_ban_detection_cooldown - After this many minutes pass after a detection, the client's detection count will be decremented, 0 to disable the cooldown (default 5)
minefix_ban_time - Minutes to ban players who have received minefix_ban_detections detections, or 0 for permanent (default 0)
minefix_ban_reason - Reason to use when banning players (default "Rocket mine exploit detected")
Watch out when you're paying people for private requests! Most stuff already exists and you can hardly assess the quality of what you'll get, and if it's worth the money.