English: Electric fence, The Links Fence controlling cattle grazing on the dunes of Holy Island. The northern part of the island is dune covered, with sand blowing off the extensive beaches running up towards the Tweed Estuary. The Tweed has brought an unwelcome guest. Piri-piri, an invasive weed from New Zealand arrived down the river from the woollen mills of the Borders. Signs warn visitor to remove the seeds from their clothing before leaving the island.