It is required that shore power (the line from the pedestal to your boat) be marine designed and properly connected. A marine shore power cord differs form your home or RV outdoor cords primarily in the boat connection side. These cords have a secure locking mechanism (usually a locking ring, though newer ones have clips). The locking mechanism provides a secure physical connection plus properly engages the weatherproof seal. 

West Marine has an excellent article on boating electrical - see #3 in their "Ten Deadly Conditions" advisory about the use of the locking ring for shore power.

See Gerry Giles for options on available marina discounts on cords, inlets and other boating accessories and supplies.