Garlon is a "better" option. It does not translocate as much as Tordon and if applied at the right time is just as effective. Honey Locust is pretty easy to kill by just girdling. Black Locust is a different beast. About the safest way to deal with Black Locust is to just let it naturally die off. You will not get , or very few, sprouts. If you remove Black Locust over story or mid story, and allow sunlight in you will be fighting thousands of stump and root sprouts. Hopefully chemical application will kill the root system also. It is not the most desirable option but it is the safest, rather than dealing with all the sprouts you may get and the cost associated in doing so.