As always, check the park website for alerts before making the trip (link above).
We suggest entering the park from Cain Highway onto West Marlton Ave. Shortly after entering you see a sign for the park - make a right and pay the $3 charge. You will place the money in an envelope and tear off a parking pass from the envelope to hang on your rearview mirror. After paying continue straight until you reach the parking lot on your right.
After parking, choose one of two ways to pick up the Perimeter Trail. At the far end of the parking lot, opposite the end you enter, is a trail head (it is easy to spot). The other trail head is located just before you enter the lot on your left. Either trail head works. If you enter one, you will exit the other.
Stay on track by following the white posts with arrows on them (see the photos below). The Perimeter Trail is essentially the only trail at the park, but there are still a few opportunities to go wrong. Follow the arrows on the posts and you should be fine.
Mountain bikers: to preserve the trail, the park asks that you do not ride when the trail is muddy. Also, heed the blind turn signs because bikers go in both directions on the trail.
The Maryland Department of Natural Resources told us that trail maps for Rosaryville are currently out of print (Feb. 2013).