If your layers are only separated from the P Rocks by a fence they have definitely been exposed but since they are all adults you may not see any issues with them. If they raise chicks, you might start to see problems with the disease in that flock then. If the Araucanas are on the other side of the house you may be lucky, but infected material can be transferred on your clothes, hair, shoes and skin so it may rear it's ugly head in that flock too at some point.
Getting unvaccinated birds (particularly grown birds) from different sources greatly increases your chances of bringing Marek's into your flock. Unfortunately, like you I didn't know that when I started out and once you realise that you have the disease it is too late.
Cleaning and vacuuming out your coop to remove all the dust will help to reduce the level of infected material and the risks to other birds..... ensure you dispose of that bedding and dust from the vacuum cleaner where it cannot re infect..... burn or bury. Virkon S is one of the few products which will kill the Marek's virus, so disinfecting the coop with that once it has been cleaned out will help. The virus is spread by infected dander dust being inhaled and this is most likely to occur in the coop. The best that you can do is reduce the reservoir of infected material. There will be some in the ground that you cannot eradicate and there will probably be some trapped in the feathers of the remaining chickens, so all you can ever do is reduce the level of infected material. I understand that, similar to cold sores in people(both are Herpes viruses), birds only shed the virus when they are symptomatic, so culling sick birds or isolating them in an area that can contain the infected material and be relatively easily cleaned up..... as described above .... and practising good biosecurity between them and your other birds ,when you have a suspect bird, is probably a good idea.
For information, the vaccine is only available in bulk in other countries too..... usually 1000 dose units and needs to be administered within an hour of the active components being mixed, so it makes the logistics of vaccinating small hatches unrealistic. The vaccine is also leaky and does not prevent the birds from getting the disease, just protects them from the more serious/fatal symptoms which may allow the virus to mutate and be responsible for the more aggressive strains of the disease that are becoming prevalent..... so vaccination may not necessarily be the best option in the long run. I have a mild version and I would rather manage that even though it means losing the odd bird than vaccinate and risk the development of a more aggressive strain. If you already have an aggressive strain, it probably pays to vaccinate.
