Unless fishing on private property you must have a fishing license.
Go to the following Maryland DNR site and see what they say about licensing in MD.
Fill, you'll need to get a MD Coastal Bay and Sport fishing license. This will cover you in both the bay and also the Atlantic Ocean Surf in Maryland. If you're fishing around the APG area then you'll definitely need one as the majority falls under the Tidal waters of the Chesapeake. Last year was the first year that you were required to have a license to fish the Ocean surf. You've always had to get a Tidal license for the Chessie.
Not everyone fishing from private property is exempt from the license requirements. This is quoted from the guide book for who is exempt on private property.
"An owner or tenant, their spouse, children or the spouses of their children residing on the property
may fish from their riparian shoreline on nontidal waters. Anglers should confirm riparian ownership
before fishing as some impoundments and waterways are surrounded by buffers; in these areas,
there are no riparian shoreline owners and fishing licenses are required. Anglers with reparian
shorelines must comply with all fishing laws and regulations."
"Fish from private property as an owner, family member of an owner and have registered with the State."
you can fish the entire Susquehanna up to the Conowingo Dam with the Coastal Bay and Sport license. If you decide to veer off the Susky into Deer Creek or Lake Octararo then you'll have to get a "Non-Tidal Freshwater License".
Go to the MD DNR site and click on the "fishing" link. there's a link there to buy your license online. I'd give it a try out there. You never know.