i'm sorry to hear of your problems!

the "symbiotic" relationship that ants have with aphids (well, it may be
more a slave-master system, im not sure!) is very interesting, although as
a grower under attack from them im sure you dont care about how interesting
it is at the moment lol

But from this document ...
http://www.sciencedaily.com/releases...1009212548.htm

It suggests that ants leave trails using their feet...

A previous replier to this thread, 0tterbot, suggested using a line of
vasoline. Whether or not that will work I dont know, but that sort of
approach seems like the way to go. I guess ants cant leave their chemical
footprints in water, nor can they swim well, so maybe a medieval-style moat
around your plants will do the trick?