I have heard of guys welding the diffs instead of buying lockers. How effective is this and does it last. I imagine it is only for trucks that dont get driven on the street.

I have a lockrite in the rear and I did a fozzy locker in the front with manual hubs you just unlock it can't tell a differance in four or two wheel drive with the hubs unlocked.  I works great only tested it on snow hills for now but when the time comes I'll let you know.  If you go solid welded then it would be like a spool your tires will chirp on tight corners but 100% locked 100% of the time.

What he said. 

It's nice because the rear end always acts the same.  You don't have to worry about it locking or unlocking, but it does put a bit more strain on your rear axles.  Make sure you have a qualified welder to weld up your differential gears, otherwise you can break the welds when out wheeling.

I recommend spending the $100 and picking up the mini-spool instead from Trail Tough.

I've seen it on here so you could try looking for it.

When you "weld" the rear end, take out the spider gears (not the ones that the axil goes through) and fill in the empty teeth with weld(the ones that are not engaged with the side gears).

This will lock the rear end because the gears will be unable to turn.

This will allow you to keep the proper temper of the metal that holds the axil and no welds to break.  You don't have to take your differential apart and reset the ring gear.  Lastly, if you don't like the rear end welded, you can change out the gears back to stock or one of the lockers that use your stock differential.

do a search for locker at Ack'e FAQ (the link is in my signature).  There are two welded locker articles in the reseulting search that might be of interest to you.