There is no way to make the little trees not come back since they will sprout from seeds in the soil and new seeds are going to come up each year. You can kill him a little seedlings however with over-the-counter herbicides by the following method.
Cut off the seedlings near the ground and then immediately paint a full strength solution of a weed killer with either glyphosate or triclopyr as the active ingredient to the cut surfaces of the "stump".
Thanks for the question. Please stop in again soon!
Q&A Library Searching Tips