Here is what I do.
Take the bones you want to use ( I use the shinbones )and if you plan on cutting them into halves, go ahead and do that. Rake out the marrow and soak the bones in a solution of water and laundry borax. Every couple days turn them around in the mix just to expose them to the borax better. After a couple weeks, give them a good scrubbing and let them air dry. Put them in a dry place for a few months and soak them in linseed oil and let that dry. All this takes time, but the results are good.