If it was an incredibly valuable structure, like the PP in _City, I walk out and martyr myself rather than have to waste time in walking back to base....so technically I seek out the deadliest foe I can find and kick him in a shins a few times and he usually is nice enough to give me a free ticket back to my base.
Now, if I'm a 'wire/Tech, I usually ensure two future kills by putting three mines at each of the entrances of the building I killed - except on maps where the mines are incredibly vital to structure defense.