Every young dog i have ever started, I did it this way. This ALWAYS gets them tracking. Now, I won't say they won't run trash, but thats another whole issue. I like to start out puppies as soon as I can. I use cooked beef fat. You can go to the store, and buy a real fatty, cheap, cut on sale, and cook it up. I cut it into several strips. I also take 1/2 of it, and cut it into tiny pieces. Use those as a treat when they do good. put the pup in a kennel, or cage where he can't see you. drag the strip on the string, in a small simple circle. Leave a small piece at the end of the trail, where he can't see it, but runs right up on it tracking. Carry the pup over to where you stated the "track". He will follow it, and find the treat. I would do this just TWICE a day. Be SURE to keep the strip of fatty meat in direct contact with the ground at first. The next day make about a 20 yard circle, if he did well on day one. If he did not do well with the track on day one, make the trail shorter. You won't believe how well they pick up on this. After two full weeks, pick up the meat, and just skip it along the grass, leaving 3 to 4 foot spacing between. This will teach him to "hunt" for the next spot. In three weeks time, I usually had mine worked up to a 50 to 75 yard trail around the house. Zig zagging around bushes, and making it difficult for him to follow it in a straight line. If he can do that, he is now ready for rabbit scent. Put rabbit scent on a rag, and use a 6 foot or longer pole with a string on it to the rag. This is to hold it out away from you so he is not following YOUR foot steps. Again, start out fairly small. Leave him a treat of his liking at the end of the "rabbit" trail. Do this for another couple of weeks. He should be ready to take out and turn him loose. When you do, take him somewhere fairly open, so he can SEE the rabbit get up and run from him.
I wish I had the time and patience to start ONE more set of beagles.