parking light flash wiring viper 5002

Another noobie question here, I've decided to run a backup battery on my system (viper 5002) but had a question on the parking lights.. Incase someone cut my wires I did not want the lights to use up the backup batt power if the main one was disconnected.. So i thought about hooking it up to a relay.. (with the main power coming from the main battery and not the brain)... I guess my main question is,

Do i need to diode isolate any of the wires for a 2000 honda s2000 with this kind of setup.? If we did, I was thinking :

parking light will have 2 power wires connected to them in essence: the regular power wire, and now another one from the relay.. Do I need to put a diode in front of each wire? So one infront of the relay, and another one infront of the regular power wire and then they join together going out to the parking lights.. or is this overkill or not necessary? or does my post doesnt make any sense?? lol

Yes, I would diode isolate the wires.  One in front of the relay and one on the regular wire then join at the parking light wire like you said.  I don't think it would be really necessary but better safe than sorry.