From the East/North:
Take I-95 South to Exit 22. Turn left onto North Benson Road/ Route 135 and continue 0.22 miles. Cross Boston Post Road/ US-1 at the light, and continue straight on South Benson Road for 0.5 miles. At the third Stop sign, South Benson Road veers to the left. Continue on South Benson for 0.2 miles. Make a right into the big parking lot. Drive past the Stop sign and park on the left.
From the West/South:
Take I-95 North to Exit 22, Round Hill Road. At the end of the ramp, go straight on Walls Drive. At the first traffic light, turn right onto North Benson Road/ Route 135 and continue 0.2 miles. Cross Boston Post Road/ US-1 at the light, and continue straight on South Benson Road for 0.5 miles. At the third Stop sign, South Benson Road veers to the left. Continue on South Benson for 0.2 miles. Make a right into the big parking lot. Drive past the Stop sign and park on the left.
Picture of one of the paths to the beach.

http://www.fairfieldbeachaccess.org/ is an active group who works hard to defend your right to walk your dogs off leash on the beach. Visit the site and browse the various offerings.

Their site features a Tide Chart which you may use to time your visit to this beautiful beach.