Its not just locking lugs you need to worry about ....but the answer is none.
Browning and Beretta have set the standard on O/U's that are durable ...with very good quality for a long time. In the Browning Citori line -- there are some guns in the $ 1,500 price range new ...that may work for you ..( and some of the better guns in the Citori line - get into $ 3,000 - $ 4,000 as well ) ...
O/U's are not inexpensive to mfg...and you have to ask yourself ...on guns that are under that $ 1,500 plateau ...why ....quality of the locking mechanism in the receiver, on the barrel, quality of the barrels, the ribs, the triggers...and what kind of warranty do they have / where do I have to send it to get it fixed, get parts, etc...
There are guns like the TriStar sold thru Cabelas and others that at least come with a 5 yr warranty ...that might work for you .../ but at least be cautious ...and understand the pricing is not just fancy wood / its in the internals that you can't see...the steel, etc..
Of course quality / durability are relative too ....do you want a gun that will last a lifetime / is a shotgun for your lifetime going to fire 10,000 shells a yr ( mine fire at least that many per yr) ...or is it 1,000 shells a yr .../ is it a gun that you expect to "use up" in 10 yrs or a gun you want to pass on to your kids or grandkids ...what is the resale value of it ( as an example a Browning Citori lightning, 12ga, 28" barrels with screw in chokes sold new in 1988 for $ 750 / today 23 yrs later...with some scratches, that gun is still worth used - having fired maybe 100,000 shells - at least $ 1,000 ). Is that value / maybe / maybe not to you ....
You have to weigh all this stuff in evaluating one O/U over another ...and cost..etc.../ and have fun with your search !