Tom Osterdock says:

both rails at the frog should be isolated, insulation. That is the side away from the points. You should also put a frog wire on the frog. This is to power the frog and the rails leading to the insulated joiners. If you are actuating the switch by motor like tortoise they have a point to power the frog and you can attach the wire to it and the tortoise will correctly power the frog as needed. some use a toggle switch to throw the switch. When changed it would send the correct power to the switch frog. I personally like frog juicers it atomatically changes the polarity and you don’t have to worry about it. the problem with frogs is that the engine traveling over frog and insulators can short the system out momentarily which will trip the DCC system off line. Changing polarity of the frog stops that problem.

Morgan Bilbo says:

I don’t use plastic joiners. I use toothpicks. Inserted properly, they will provide insulation without what to me is unsightly plastic sticking out. But all the above is also correct, you need to make that decision on one or both rails.