Lionel cattle corral using accessory power

If you want to use accessory power for your stockyard, you do not need to isolate the base from the track or do any of the other things you are talking about with the tape.  The common/ground is acquired from the track's contact to the base as well as the wire going to the non-insulated binding post.  If you are using a different transformer, just be sure that the accessory transformer is in phase with the track power transformer.

Now to power the stockyard by separate accessory power, you just need to connect a wire from the accessory power post on the transformer to the insulated binding post (shown below with the black circle of insulation around it) with an inline on/off switch.  It is recommended that you also wire a common/ground wire to the non-insulated binding post (although it is not 100% necessary as mentioned above because common/ground is also acquired from the track touching the base, another solid ground contact will not hurt anything).  

Also here is a wiring diagram to help understand how the whole thing works.

Does this make sense now?

 

I am wondering if the unit can be powered using accessory power...

Absolutely! In fact, for many years this is the only way I've ever done it.

JD2035RR, thank you very much for the detailed response and JOHNSTRAINS for your confirmation that the schematic has been working for you over the years.