More than two dozen campaigners braved gales and torrential rain to call for more land to be included in the proposed South Downs national park.
Protesters gathered in Arundel and walked part of the route of the town's axed bypass, which they want inside the new park.
The Countryside Agency has already begun consulting on the boundary changes after Transport Secretary Alistair Darling rejected the road.
The route of the bypass would have taken an arcing line south of Arundel, crossed the Arun valley and cut through ancient woodland.
John Clarke, of pressure group Protect Our Woodland, which organised yesterday's walk, said the park's boundary line should be moved south and the woods included.
He said: "It is extremely important the boundary goes to the railway line in order to protect the water meadows south of Arundel.
"It would also protect the magnificent landscape and views of the Arun valley, together with the ancient woodland complex of Tortington Common and Binsted woods."
Campaigners criticised councils which are preparing to fight the national park proposals at a public inquiry.
Meanwhile, ramblers are organising a series of walks to highlight areas they say should become part of the proposed national park.
On the eve of the public inquiry into the proposed park, which starts at the Chatsworth Hotel, The Steine, Worthing, on Monday next week, a nine-mile walk is to take place through some of the countryside included within the park's proposed borders.
The first walk will start from the Woolbeding Common car park, three miles north of Midhurst, on Sunday at 10am.
Organiser Owen Plunkett said: "These walks are designed to show the public the beauty of the South Downs.
"Although we are pleased most of the local authorities involved now support the creation of the park, there are still a few who remain bitterly opposed.
"We very much hope local people will join us to show their support for the future national park."
For details of the walks, call Mr Plunkett on 02392 254959 or email owen.plunkett@which.net
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article