Hey there - I had the same problem. Replaced the belt, random squeeling came back which I ignored and then saw the alternator light come on - checked and yep, I'd destroyed my second belt. Put another one on and had it tighter this time but still squeeled every now and then. Took it to mechanic and they tightened it even further, and I've had no worries since
As far as I can tell mine's not overtightened, I think I was being too cautious, plus with that massive torque I think the alternator must have moved a bit when tension came on the belt
Out of interest what belt did you use? Repco had to guess based on a landrover.. Ended up with a Gates XL 11A1130
cheers,
Ray