I'm a glider pilot, so I do FUSTAL around when I enter downwind: flaps, undercarriage, speed, trim, airbrakes, look.
Just checking won't save you 100% of the time, though. My partner once forgot to retract the gear earlier in a flight, then came in to land and did the U part by moving the lever to the other position. I think the stripe he painted down the runway cost about $50/foot. Fortunately the repair was great and it's good as new.
I'm currently in the latter category and trying my damndest to stay there, but the odds don't seem good.