The ownership of a dog can be transferred in the same manner as other property. In some cases, it can be unclear whether a transfer has taken place. For example, some rescue groups commonly include clauses in their agreements with consumers, saying that the rescue retains ownership for a period of time, or has the right to reclaim the dog (in other words, a right of control or dominion that is one of the acts or incidents of ownership). In some cases, a person who has cared for a dog for a significant period of time might want to be considered to be its owner, or need to be considered its owner, such as when the dog has a terminal, wasting illness and should be euthanized.
Ownership of a dog can be fixed by a clearly written agreement. Minimum requirements for such agreements can be found at Adoption Organization Liability for Dog Bites. When a dog owner wants to retain ownership of his dog, but has to board it with another person for a significant period of time, issues relating not only to ownership but also veterinary care and other special requirements of the dog can be dealt with by a written agreement, such the Agreement for the Temporary Care of a Pet, drafted by Attorney Kenneth Phillips (and available for free by clicking the link).