I hope I don't offended, honestly, the words "shared custody" applied to an animal seem just downright strange to me. Either take your pooch to a kennel for over nighters or extended stays if no friends can help out or rethink getting a dog at all. Take it from someone that genuinely understands the commitment a dog requires and is willing and able to give it. While I travel my sister in law or my brother will usually take care of Lambo and Hercules but often I will take them to a vet that looks after them in the kennel. Yes, it may sound cruel to leave my boys for a week or longer but they are very professional and I pay them to bathe them the day before I come back. Since the owners are Vets I feel more comfortable that if there ever is a medical emergency they will be with the proper person to handle the scenario.
Pet owners take this responsibility out of a want for companionship and love in their heart. We give to our pets and we get back. So decide now if you are up for pet ownership and for the long haul. If not or you are not sure if you have the friends and back up or not willing to spend the money required for a high quality kennel during your long travels, do the dog a favor - DON'T! That dog can find a new owner with all the right environment for a happy life. Personally I think traveling 3 or 4 weeks at one shot would be kind of long for my boys but shorter stays 3 or 4 times yearly shouldn't be an issue. Well, this is my personal opinion and I am sure many here will be outraged of even thinking of leaving their babies in a kennel. Hey, different folks, different strokes.