How about for a cooldown mine give it 10 seconds added to all cooldowns. This just gets added and doesn't go away. So even if you have 35 seconds left and it goes to 45 you just lost those 10 seconds. Might give you those extra seconds when running away form a regulus with snipe.
Also like a mana mine which could just instantly drain a percentage of mana.
For this i'd like to see maybe 3 or 4 differant kinds. To destroy you'd need minions and an item that would give line of sight/visibility of them. Creeps and minions wouldn't set these off so they could get within range of them. For assassins we'd add a dearm trap abilities similar in area to where the generals minions are so they could dearm them. Maybe a 5 second cast and no cooldown. Because if people are blowing money on them you don't want to make them too easy to destroy.
There also would need to be a limit for the number of mines of each kind you would have out. No limit to how many mines only what kind.
My ideas for traps:
Mana mine: Drains 10% (25%) mana from target. (artifact version in parenthesis) - 250g (600g) - limit 5
Cooldown mine: Adds 10 (25) to all cooldowns regardless of if a cooldown is active. -400g (1000g) - limit 5
Line-of-sight sentry: This mine doesn't blow up but gives line of sight. Would last 2 or 3 minutes and would be destrucable. Only one active per demigod. Something like 20 line of sight for regular and 30-40 for artifact version. -100g (200g) - limit 1
Damage/slow mine: Great way to add tactics to the game. Pop 5 of these guys down and run an enemy into them trying to get away from you. Great way to kill if they are faster than you and adds more tactical strategy to the game. Slows by 40% (60%) for 10 (15) seconds and does 200 (400) damage. -400g (800g) - limit 3 - Wanted to keep this expensive so that regulus's mines are still more effective and more easily used. Couldn't have too many of these.
Burn mine: Causes some heavy DoT. Most expensive mine and only availible at the artifact shop. Sets target on fire dealing 80 damage every second for 15 seconds. - 1200g - This mine would also set enemy creeps on fire for 40 damage every remaining second of the main targets cooldown as the target passes by them creeps can't set other creeps on fire. Potential to be similar to plague but at the end of the 15 seconds everything would stop instead of a never ending chain reaction. Could very idealy be a finisher in addition to damage/slow mine.