Bull ants are very persistent and have out lasted and out smarted me
more than once.  Doing war with them requires constancy.  I've been
advised by local 'oldtimers" that Bull ants live in wood so the first
thing to do is remove any dead wood or debris from the surrounding
area..  Then to try greases and other ploys.  But, probably the best
advice I received was simply "to move the hives".  Sad-maybe, but it
worked.  Regards, George.