Power board help

[rooly1983]

Hello, I'm currently working on my first PCB for a small robot. I would like to explain what I need to achieve and the solutions I've come up with so I could get some advice as to the best way to go about my problem.

The power PCB that I'm designing takes in 16.8V from my 14 Ni-mH battery pack, and outputs 5V and 12V using LM2678 voltage regulators. This 16.8V from the battery is also connected to 6 motor controllers which powers 6 motors, the max current draw this line will ever see is about 6-9A.
What I would like to do is have a relay setup on the line to the motor controllers which is controlled by a signal from an arduino. The arduino will send 5V from a digital output when a killswitch thread is called, this will disconnect power to the motors without killing the 5V and 12V lines. What do you think is the most efficient way to do this?
Currently, the problem I face is I havn't found a relay that has a switching voltage of 5V and can handle up to 9A. The relay I have on hand is from radioshack, it has a 12V activation and handles up to 30A. The idea I had was to mount a small relay on my power PCB that is tied to the 12V line which is activated by my arduino signal. This 12V would then be routed to the larger relay which would disconnect power to my motor controllers. There seems like a much easier way of doing this.

Also, please take a look at my board. Its my first so please give any feedback, I'll definitely use it. The space on the right side of the board is where I was planning on putting the small relay tied to the 12V line, the larger relay attached to the motor controller line would plug into that. Don't pay attention to the LED plug either, thats for another board with my status lights.