Location of Bank 1 Sensor 1 O2 sensor on a 2004 Buick Lesabre
 

My 2004 Buick Lesabre recently threw a P0135 code signifying the Bank 1 Sensor 1 O2 sensor is not working properly. However, I'm having a hard time locating the o2 sensor myself. I looked up the car and there was an o2 sensor directly before the catalytic converter, but it was covered by a pretty intense debris shield which would require some destruction of the rivets holding the shield in place to get to the 02 sensor. However, I have also seen some videos in which this sensor is located behind the engine and accessible through the hood and the o2 sensor is removed with a socket that has a slit for the wiring harness connecting the sensor. Does anyone know where this sensor is located so I can prep the fix accordingly? Additionally, if it is the 02 sensor located behind the debris shield, how do you go about removing the debris shield to access the sensor? My plan was to dremel off the rivets holding it on, replace the sensor, then use a rivet gun to reinstall the debris shield.