I can make couplers - one with two links, three links, or with two links and a third link that would be removeable.
The problem that a lot of people have with couplers is the dogs getting tangled, crossed, one pulling the other, etc. Successful use of a coupler requires that each dog be trained to walk nicely on a leash and to respond to voice commands BEFORE putting them together.
I learned about teaming two up before each was trained with the miniature horses I was teaching to drive.
No one was hurt but it wasn't pretty
. Now my rules are each member of a team must be trained BETTER than if they were to be used as a single -- same rules applies to dogs.