A good way to get UFO's is build 4 bases in a square so something like
X ---- X
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X ---- X
X's being the bases.. And then;
X -u-- X
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X ---- X
U being a UFO, here you have a choice, send your top right interceptors at it, it'll flush the UFO towards the other base, after you send those interceptors out, bring your interceptors from the top left, so
X>-U< X
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X ---- X
The > and < being interceptors, this way it flushes UFO into the other base, and in the square you can flush a UFO into another base 80% of the time, only problem is timing when you intercept them to keep you from making those punks hit the drink when yah down them.
Happy hunting.