I plan on putting up a split rail fence. I have looked for alternative materials but have found none in the split rail catagory. My question is when I put the cedar post in the ground how do I keep them from rotting and how do I keep insects away from them. If you know of another material that is visually attractive to use in the split rail fence please tell me.
You can protect cedar posts by soaking the ends in a bucket filled with copper napthenate (Jasco, Copper Green Wood Preservative and others). It takes time for the chemical to fully penetrate, but a soaking treatment will deter pests and water rot for years. Be sure to do this where you will not stain concrete or kill plants. Copper napthalate stains, smells bad and is toxic. Observe appropriate precautions. You may want to search "copper napthenate MSDS" for more information on this pesticide / fungicide.
If you are using Red Cedar post they will last about 15 to 20 years (Western Red Cedar). A lot of the non-aromatic cedars are not very decay resistant. If you can smell the Cedar then it is aromatic and will resist decay. Western Red Cedar naturally resists rotting and insects, resulting in a durable, long-lasting fence system. All wood will rote eventually .To extend life of post using PT or Cedar make sure that you have about 2 inches of gravel at the bottom of the post hole. This allows for drainage. The hole should be about 3 feet deep depending on your frost line. Also I would not use concrete in the hole around the Cedar post. Concrete absorbs water, which will lead to a faster decay of the wood.