I needed some preservative and on investigation I found several alternative types.
1. There is creosote if you can get it, but as has been said - it stinks.
2. There are the Cuprinol type products that are spirit based and available in different shades. Usually quite expensive although I have found Blackfriar and Barretine to be cheaper than the big names.
3. There is a Cuprinol brand product which I have used and which is not the spirit based type. I bought it from premiumpaints2 on ebay (Cuprinol Exterior Wood Preserver 25 LITRE -GOLDEN BROWN) and it cost about £60 for a 25 litre drum. Strange stuff though, goes on like water (water based so I suppose that is fair enough!!) and looks seriously grott. Then the colour seems to develop after 10 mins or so.
4. I also tried a product called Lumberjacks by Everbuild, and that was ot spirit based either, completely clear finish.
5. Finally there is the cheap, ghastly fence treatment that is a waxy sort of finish that repels water but blocks the grain of the wood completely.
Which is best? Well the thing is you don't get to find out until several years have gone by and the timber is still good (or starting to rot), by which time you have probably forgotten which treatment you used anyway so you can't compare. In that respect this post may not help, but it does at least tell you what is available. Personally I would avoid the waxy stuff but any of the others seem to be advertised as good for the job and the Cuprinol from ebay was comparatively economical - an important consideration for the volume you will need.
K