Well, being a kiwi also, I have the same problem, especially with mums new mare who had horrendous hooves when we got her. I use worlds best hoof oil on all 3 of my horses (one barefoot tb, one front shod tb, one barefoot miniature) and I would never use anything else after finding that stuff, it's just brilliant. When my gelding first arrived here 2 years ago, the last farrier he saw before we got him gave him a bit much of a "trim" and he developed growth rings or whatever theyre called and had horrible hooves for around a year while that all grew out and got trimmed properly (I love my farrier, I love my farrier..) However, unfortunately for me, as I move into the manawatu very soon I will have to find a new farrier -_-
If you can try to keep a puddle around his water trough you should be alright, but honestly, the worlds best hoof oil is amazing for cracks and moisture etc, and I second the suggestions of diet etc, if you can get bloods to find out the levels or everything that would be a good place to start so you know what to change and what to keep the same.
R.I.P ~ Bubbles - 25yo tb mare - 13.04.2011 ~ 8:30am ~ passed away naturally and peacefully in my arms