If you do, you could try putting food out in the area they are....and keep moving it closer and closer to your farm. It may take some time to do it, but I have done this in the past with success to have a feral cat come to my door for food. And if it doesn't work, you are not feeding them close enough to your farm to cause a problem with the other critters. You will have to stay far from the food for them to even consider approaching it though.
Dog chews---I have never had a dog so can't be sure if there are problems with this, but there are synthetic products out there. From the ASPCA website:
Durable chew products typically are manufactured from plastics, including nylon and other synthetic polymers impregnated with flavorings. These products are well suited for aggressive chewers. Pet parents should choose a product size consistent with their pet’s size and chewing habits. Dogs who find these chews desirable will slowly wear down the ends of the chews, resulting in thin sections that can be broken off and swallowed. Guardians should discard these chews before they become excessively worn.
http://www.aspca.org/About-Us/policy-positions/dog-chews-treats
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