Hi guys. Just built my first fixie. First thing is I noticed is that i keep accidentally freewheeling and undoing the sprocket off the hub. I don't have a lockring (thought the sprocket came with one, but it didn't).

Do I need a lockring, or can I just tighten the sprocket very tight by pedalling uphill or something? Ideally, I would like to not use a lockring, as it means I can use the extra few mm to improve the chain line.