Fort Foster is a wicked cool spot, so I go there a lot (I'm a webmaster AND a poet!).
Not many dog-friendly beaches in Maine have:
A long pier for pier-walking (but no pier diving, please)
Miles of hiking trails open year round
Pavilions for special event rentals
Windsurfing and kayaking
Grills and picnic tables for public use
Really interesting military fortifications for exploring
But Fort Foster does.
This is not a a surfing beach -- there are few large waves here at the mouth of the Piscataqua river, and there's that big pier to accidentally whack into, but that makes it just fine for those who aren't looking show off their surfing skills. Lovely place for stand up paddleboards!
There are great views of the naval traffic at Portsmouth Harbor, views of Whaleback Lighthouse, Portsmouth Harbor Lighthouse and Fort Constitution. There is a designated area for scuba diving, windsurfing, and kayaking but trailers aren’t allowed in the park.
Leashed dogs are allowed here, and this is one of the main reasons I visit the park year round. The park is closed to vehicle traffic in the off season, and a walk on the beaches or well-groomed hiking trails with your canine buddy is pretty spectacular in the fall or on a crisp winter's day.
Location: Route 103 to Gerrish Island Road to Pocahontas Road, Kittery Point, ME. Hours: 10:00 a.m. to 8:00 p.m. Day Pass: $10 per carload at the gate (May to October).