Radial decoupler, my greatest nemesis.

[lazarus1024]

If I need them I almost always just stick them on the top of the tank pointed with the exhaust inward.

9 times out of 10 that is enough. It kicks the top of the tanks outward, which is usually the part that ends up colliding with part of my rocket.

Occasionally if I need more I'll mount a pair on each side of the tank near midline or two at the top of the tank next to each other.

[allmappedout]

I really wish that you could use paired decouplers, so having a large tank having one attach point at the top, and one at the bottom. What seems to happen when you try this is that the unattached decoupler applies a much bigger force to what appears to be 'inside' the fuel tank as they're not connected and clip a lot.

[urablahblah]

For what it's worth, there is currently a bug with decouplers where they apply no ejection force if the part is also strutted. Hence the need for sepratrons where you might not normally think they would be needed.

I never noticed this until career mode before I had unlocked struts. It surprised me the first time I decoupled and the spent stage when speeding away. I had forgotten how cool it looked!

[toomuchbrew]

I hardly ever put selatrons at the center of mass. I put them near the top. Sometimes on both sides so the tank flies away, top first and I don't have any issues. I did once have two tanks collide, the trons broke loose and hit the tank that still had fuel. Explosion time. I more often put trons on one side at the top and the tank spins away on its long axis.