Cocktail baits have always worked for me.
Combinations of; lugworm, ragworm, mussel, razorfish, squid and mackerel.
Fish them on pennel rigs using good quality hooks, my preference is for 4/0 Vikings.
Tie your rigs up so that the hooklength (40lb) comes off the trace (50lb) a couple of inches above the rotten bottom link, and keep the rotten bottom itself (20lb)quite short. Stick to at least 30lb mainline.
This keeps your bait hard on the bottom where the cod will be feeding.
Plan your trip around the weather reports.
If it's been rough for a few days look to fish the Harbour, Bally's or the cliffs on a rising tide.
If it's been calm for days beforehand plan to go to the rock marks and aim to fish down to low tide and some of the flood. beware of being cut off on exposed marks by the incoming tide, always make sure that you retreat safely before gullies flood behind you.
Bigger tides are better for either option.
I haven't found the ground too snaggy at the harbour, but I'd still go with the rotten bottoms as there are one or two snaggier areas.