I'm a big nerd, so when I saw 'Ring' as the prompt, I immediately thought of 'Der Ring des Nibelungen'! What? You thought I'd think of Lord of the Rings? Bah! Too mainstream, normie!
Originally I wanted to make the eponymous Ring, but the cursed ring that lets you control the world but destroys you overtime wasn't something I had an idea how to represent in Magic. But there's another ring in Der Ring...
At the end of 'Die Walküre', the 2nd part of the cycle, Wotan seals a sleeping Brünnhilde behind a perpetual circle of fire that was only breachable by the bravest of heroes, to protect her from being preyed upon by the unworthy (it's worth pointing out that Wotan sentenced her to that fate in the first place, and the fire was only added after Brünnhilde pointed out he was being really damn harsh - Wotan's a jerk!).
So here, the card protects a creature you have from whatever but seals them away, and only a brave creature (non-Coward) approaching can release them. I decided that such a narrow card needed to be cheap and as easily cast as possible, so hybrid mana appears! The effect is very white, but I made it Red/White because Fire, and the reference to the Coward type, which mostly appears on Red cards.