I have very long hair myself almost to my tailbone and I apply the same principles to my dogs' hair as I do my own:
1. Use coconut or argan oil to condition the hair
2. Supplement the diet salmon oil/fish oil. I've had great success with salmon/fish oil because it is more biologically available to dogs than flax seed and the dog's system can absorb more of the omegas.
3. Adjust the diet to deliver enough proteins and oils (for my dogs this meant a prey model raw diet and for myself a paleo-type diet).
4. Don't wash the hair too frequently or with harsh shampoos. Conditioner takes longer, but it is just as effective in cleaning hair as shampoo is. I rarely use shampoo on my own hair because it dries and thins it out. If I just use conditioner, the strands are considerably stronger, more flexible and thicker. So I do a conditioner only wash by applying conditioner and leaving it in for at least 5 minutes. When I have to wash the hair with shampoo due to build up, I coat the lengths with a mixture of coconut oil and conditioner. This works very well to keep the ends from drying out.
I'm happy with our regime because the dogs' hair look and feel amazing, they don't need harsh baths as often as they used to and they have more hair than I know what to do with.
