You should place lines instead of tracks. Put it on the top/bottom copper and the soldermask. Tracks might work, but make sure to turn off "automatically remove loops". You probably know that the guard ring is only working, if the voltage difference between the senistive node (*pcb junction) and the guard node are the same voltage. So the guard ring is driven by something, like an opamp. I usually use the "VCC power port" to name the guard ring.