1999 Mercury Cougar Transmission Leak

We were driving on a trip. After a while the transaxle warning light came on. We could smell transmission fluid. We added some more fluid and continued driving to our destination. On our way home the light came back on so we pulled over. When we opened the hood we noticed transmission fluid all over the engine compartment. We put another quart in since we had to get home. We were driving on the highway for quite a ways. It doesnt seam to be leaking to bad because it wasnt slipping. I think it might only be leaking while at high rpms. Not sure though. I dont think it leaks while in park and turned off. Any clue?