Everything we do requires a single domain so I can't do that and I don't want to update everything on the ISPs, so that won't work either.
Well, again, maybe someone else will have a better solution for you, I've been working with DNS for several years but I don't pretend to know everthing about it. But if not, then you may need to adapt what you think you need to what is possible.
It's shouldn't be a big deal to slurp over the zone file periodically from the ISP and then add whatever entries you need to it. That's something you could even script. You could keep your internal entries in a file that you edit, and then have a script that grabs the ISP's zone file and adds those entries of yours to it.
Rich
