I love ARPA, and there are a number of other useful tools that can be brought to bear.
But I teach my mates to always fall back on a virtually fail-safe basic radar method: a simple line and a ring (even on an unstabilized radar) will seldom let you down. Put an EBL and a VRM ring on a target and watch. If the target moves (exactly or more-or-less, doesn’t matter which) down that line you WILL collide or come very close to doing so unless somebody (either or both) does something to remedy the CBDR situation.
No guessing, no algorithms, no bullshit. And no way to really screw it up accidentally unless you’re just one of those people that can find their way into an accident no matter what. Putting the radar into unstabilized mode eliminates the possibility of a drifting gyro inducing an error. If visibility permits you can and should use your 
to double-check what the radar is telling you, or vice-versa. CBDR is CBDR, no matter how you cut it. You’ve got to do something to resolve it.