Oxygen Sensors Short-lived!

[dantept]

'96 SVX:
For the last 3 years, I have experienced several oxygen sensor failures, both front and rear. First, the rear sensor had to be replaced twice within 8 months and 1200 miles. (I am retired and annual mileage on this car is very low absent business use!) 1 year and 800 miles later, a front sensor went. 100 miles later, the wiring harness to an oxygen sensor (I don't know which) had to be replaced. 22 months and 1000 miles after the 2nd rear sensor was replaced, it triggered the CEL again. The dealer cleared the code, and 200 miles later, it did it again. The dealer - usually reliable - can find no reason despite checking with Subaru. Any ideas? (And no, I am not inclined to replace them myself.)