I'd echo what's been said above.

I'll even flip the tire "inside out" and feel around inside and out once again if problems persist. Sometimes you can see or feel something once the strain on the tire has changed. Also look at and feel the rim and rimstrip very well. Look to see if the puncture happens at the same place every time.

I usually look my tires over pretty well before bringing the bike in after a ride. I still got my last two goathead thorn punctures after I had moved to San Jose from Albuquerque. Clearly, I brought those sons of *****es with me!