Viejo And The Hunted Ranger by Cliff Hudgins
Something is amiss. The Texas Ranger is tracking a band of rustlers and realizes someone is tracking him. He must deputize a young man to watch his back trail, while he concentrates on the rustlers. Several people are out to ambush him. It will take every bit of knowledge, courage, and determination, of both the Ranger and the deputy, to solve this two fold dilemma.