I agree.
We were looking after a black lab for the past couple of weeks (I've written before about how we 'foster' dogs through an organisation called
Barking Mad). It's so difficult to get black/dark dogs in action properly exposed. The one we had loved swimming and would jump off a bank, etc anything up to 4/5 (1.5m) high straight into water.
How were you focusing? I've just set one of the Custom Settings option on my Canon 40D to AI Servo. Haven't used it all previously, but have been trying to get to grips with it.