I do fecal exam (you don't even have to go with the vet, but instead send all poops directly to the lab - that's what I usually do, cost me $7.50/horse (+ shipping $5 for all together)). If nothing is found I still deworm 2-3 times/year, because for some worms (like tape-worms) they don't really "exam", so you have to do the prevention.
"Life isn't about waiting for the storm to pass: it's about learning to dance in the rain..."
"When we are no longer able to change a situation - we are challenged to change ourselves."
"How people treat you is their karma; how you react is yours."