This isn't an advertisment, but I thought I'd mention the very efficient service and good prices obtained from the Wood Finishers Direct web site (www.wood-finishes-direct.com). Having seen the astonishing prices asked for decking oil and wood preservative quoted by better known retailers, I was pleased to find this supplier with more reasonable costs (other similar suppliers are available no doubt).
At present, spending over £50, there's free next day delivery and a 5% reduction off the current order price. The courier (DPD) delivered in the middle of a one hour slot, as notified by email and on their tracking web site. I've now run out of excuses for not doing some fence preserving!