I don't know US laws, I know they're very different from UK laws where custody is concerned, but I'll second the importance of keeping an accurate log of ALL events, good, bad or indifferent concerning your kids and their dad.
Keep it factual and don't include your feelings, unless it's genuine fear for your childrens safety.
A (UK) solicitor told me that theres a lot of weight in these logs because it shows one parent has 'bothered' to keep the record of what happens and if it all reads the same and includes dates where other agencies (police etc) then it's one of the best gauges they can get (they being the courts)
I still keep one for Joe, and I include all contact, letters, gifts, money gifts, phone calls and times, visits, in fact anything at all concerning him and contact however indirect with this person.
I don't put anything personal in it, like how it makes me feel or what I think of it. I come here for that, or write it in my own diary/journal.