boxster cel/o2 sensor

[dzls rok]

hello all,

my bro-in-law has a non s boxster. he keeps getting cel's. each time it is an o2 sensor...and each time it is a different one. the previous owner had them changed. his mech. told him to just drive it hard and it should clear it up. he thinks its because he drives it too mild. any second opinions/ideas?

thanks