I'm always amazed when I find something of considerable size near my own neck of the woods that hasn't been visited before. Given that it's horribly overgrown and at least half of it is inaccessible (unless you're a paying visitor to Arundel Castle) maybe it's not so surprising. The part you can access on the western side of the A284 can be reached by parking at the cafe carpark where all the local bikers meet at the weekend just off the roundabout and then walking south west along the A29 till you come to a footpath which brings you up into Rewell Wood. There are actually two quite substantial parallel dykes here with a ditch between them and they run for about 1/4 of a mile on this side and about 1/2 mile on the Arundel Estate side. Whether this was simply a boundary marker or some sort of defensive earthwork is hard to ascertain, but I think the latter due to it's size and the fact that the high ground of Rewell Wood is littered with former settlements. A recent dig by Worthing Archaeological Society at Goblestubbs Copse 1 1/2 miles south west discovered remains of late Iron Age settlements in the relatively untouched woodlands. Anyway, worth visiting if you like thrashing about in the undergrowth like a mad person.