Intermittent Check Engine Light

[izzrock]

I've got a 97 4Runner with 115K miles. Last year I had two O2 sensors replaced and this year 1 was replaced. I was told that there are three total. I'm not sure if all three originals were replaced or not. I'm being told that the an O2 sensor is the cause of the Check Engine Light comming on again. This is starting to get very costly and I can see the O2 sensor going bad soo f@#%ing fast. Could their be a cause for the O2 sesor going bad so quickly??