Arduino = 12V (40mA)
Repellers = 6V + 6V= 12V (200mA +200mA = 400mA).
do you know that arduino can be powered from as low as 7vdc to a max of 12vdc. since its going to be a mobile setup, why waste your precious power giving the arduino 12VDC.
the repeller part when you say 6 v +6V it means your hooking it up in series. but then when you did the current calculation, it means that your hooking it up in parallel. so which one is actually your setup?