You might want to check out blood trailing training information from the JGHV (umbrella training group for the versatile breeds in Germany)--there are some good ideas/tips there as blood tracking is a part of their testing system you can google up. "Tracking Dogs for Finding Wounded Deer" a book by John Jeanneney is about as good as it gets for a resource. Ideally you need blood, a way of dripping or dabbing it, a deer hide and a way to mark the trail so that you can follow it without the dog knowing. My dog was more interested in other smells than the deer blood but once he figured out what I wanted and was rewarding and particularly once he started recovering real deer, he has gotten into it and we have had good success. If you deer hunt or have friends that do, you can also ask them to give your dog a chance to track even where they don't need it (especially when they don't need it because if they do need it most likely someone has walked all over the start of the trail).