dc42:
All you need is a single supply providing 6.5 to 7V and capable of supplying 500 mA or more. This can drive the Arduino and both repellers. If you are worried that this is a little too much voltage for the repellers, you can connect a silicon diode in series with each one to reduce the voltage by around 1V.
Thanks for the reply, that was very informative. Let me try the arrangement and i ll get back.