Locust trees can be a growing problem, especially when grown as shrubs. As a matter of fact, locust trees have been tagged as invasive in some US states like Michigan, Oregon, and Washington.
They have sturdy, rhizomatic roots that easily follow a long stretch. While they are good at controlling erosion, they could also be a problem for critters in riverbanks as they block the passage or flow of water in the river. With these, it is not a wonder why some would want to stop the spreading of locust trees.
There are two ways to stop a locust tree from spreading. One, their aggressive growth can be stopped through repeated cutting specifically during the growing season. New stems should also be cut during this time. This process should be repeated for many years to finally stop them from spreading.
Two, you can use potent herbicides. Cutting the tree horizontally during late summer and early fall for the herbicide to trickle down to the roots help in stopping the locust tree from spreading. This is not a one-time big-time thing, however. Like the first step, applying herbicides must be done twice a year for at least three consecutive years.