Lighthouse in Dominion:Seaside costs only 2 yet is a duration card that provides +1 Action on the first turn and +1 coin per turn it is active. On top of that it provides protection against any attack cards while it activated.
It seems to me this is an incredibly powerful card for being worth only 2. If backed up by a couple higher coin you could easily get 8 coin and buy provinces. All the while you are protected from any immediate threats. The main advantage IMO is gained from having +1 each turn. This adds a lot to a players buying power.
So what can you do to stop someone from abusing this card?