I used to photograph Afghan hounds on various tracks. so maybe these tips may help a bit
first of all you will need a "fast " lens and fast shutter speed so get used to setting thjat up it will help
Ok your at the track but where do you stand? well one place is not square on to the track, try and get on a bend whee the dogs are approaching
The determination in the dogs eyes makes wonderful photos
That gives you time to sort out DOF using the running rail as a guide
Not only that but also allows a bit more time to get the dogs in view
below is a poor example but to give some idea of how much more time you get. the shot
as you can see even if the dogs are some distance apart you can still get them all in frame
This though demonstrates the advantage of getting on the bend of the track
Square on presents 2 problems
! do you pan and follow a dog until it is level with you and only get the one dog and a blurred background
2 fix the spot the dog is going to pass and have a blurred moving dog
Fast lens and fast shutter speed. see the eye deternination
or you could go for out of the traps shot
I posted bad photos so not worth copying