You can dig holes and set standard cyclone fence poles in concrete; then you can bolt wood to the posts and attach the rest of your wooden fence to that. Or, you can buy "saddles" for 4X4 posts: one end gets set in concrete, and then the saddle end is bolted to the bottom of the post. Or, you can set short galvanized poles in concrete, let them stick up about 12-18", bore out the bottom of your 4X4 to match the size of the post, then bolt through the post and pipe at the bottom. Just make sure you dig big enough and deep enough holes so that you have adequate concrete supporting the fence. If you skimp, you'll have a leaning fence in a short while...

I am not sure where you live, or how you want the fence to look, but in all most all pastures in Kansas we use hedge. Google Osage Orange or hedge. It will last for almost ever. It is very hard and doesn't rot easily. If you want barb wire or woven wire fence it is another way to look.

You won't find hedge at a farm store, you will have to ask around.

Carajon: You are right about the cedar, but may be too concerned about the pressure treated. If it's throughly sealed with any good penetrating oil stain and allowed to dry completely before being used, it's not going to harm your blackberries.

Just don't set them in concrete, because it will hold moisture against the wood and not allow it to drain properly, which is the primary reason for rot. We learned that the hard way before we started using longer posts and deeper holes, with gravel at the bottom and around the base of the posts. Then, just backfill with soil and pack firmly.

The galvanized steel posts set in concrete with wood bolted to them for attaching the fence panels are an excellent option and would last literally forever. However, it's also a matter of how much you are planning to spend and the desired appearance. If it's along side your driveway; should we presume it's also near or next to your house?