We use locust posts and hemlock rails for our split rail fence.  The posts are spaced 10' apart and are tamped solidly at least 2' into the ground.  We do not use concrete for split rail.  Split rail fence comes in 2 rail (about 3' high) or 3 rail (about 4' high).  Gates can be built onto split rail fence.  Also, welded wire can be attached to keep pets in.