The best way to get there from the north is to take 36 to Lackey Old State Rd. It's about halfway between I-71 and Delaware. Follow the signs for the Marina.
Head south on Lackey Old State until you get to Hollenback Rd. It'll be the 2nd stop sign.
Make a left onto Hollenback and follow the drive back toward the marina. You may have to park at the dog park and walk on back to the marina, but you'll probably be able to get to the dockside by car.
It's a beautiful spot, good luck!