Bobcats are ruthless and cunning.  Much of the standard security measures will not work.  They will even slip into a fenced in area with a person and four dogs inside if they see an opportunity.  That is until a bird makes a noise; then the chase is on.
I agree a Pyr makes a great guard dog, but Pyr puppies can be a handful and a little too ruff with the birds.  Great Pyrenees do not mature until they are about 1.5 to 2 years old.  Hence, I would suggest the following:
Make a fenced in area for the chickens.  Find a guard dog and keep the guard dog on the perimeter of the chicken yard.  To keep the dog from running loose, this works best in large fenced in area.  So, basically you have need a fenced in area with a smaller fenced in area for the birds.  Never ever tie up you dog outside, they must be free to move about.
The dog you need is a guard dog that can take the weather and doesnt need a huge amount of people interaction.  Hence, why the Great Pyrenees and other LGDs (Livestock Guardian Dogs) work out so well; they were breed for this. Check out 
www.dogbreedinfo.com and 
www.lgd.org.  If you can keep the birds and dog separate, I would suggest an older Pyr or German Sheppard or another weatherproof guard dog breed.  Hunting and companion dogs may not work out very well.
Also, just because you find a breed good at guarding doesnt mean they do well.  Temperament is even more important.  And, any new dog will need to be trained to ignore the chickens and to learn to obet you.  
All of this means lots of work for you, so get ready.  I let my guard down for a couple of days and the bobcat started to show and kept coming back.  
Good luck,
Jim