
A friend of mine home boards. She choses which dogs she boards (e.g. neutered, not aggressive, etc). If for any reason the dogs don't get on, then the house can be split into three by closing baby gates and the garden is split into two for the same reason!
New dogs spend one night there before any booked boarding to make sure they are ok.
When my friends have to go out together, then any dogs get split up into different rooms (or crated if the dog is used to it in some cases) unless they know the dogs really well and know they get on.