Insert Expletive about Oxalis pes-caprae Here

Google "oxalis weed" and you will find a slew of frustrated gardeners.  Oxalis makes nuns spit and pushes even the hippiest of hippies to search for nuclear arms in order to destroy it forever..  And for good reason:  Oxalis has a long, fragile taproot with the tiniest of bulblets at the end.  Pull out the root and I swear the next day you will find the same plant smiling back at you defiantly.  Let it flower and seed and the sucker will throw the seeds 6 feet away, distributing new nurseries of evil sulfur flowers. 
Some people go to the trouble of carting away the first few inches of their soil and starting fresh.  This usually doesn't work because the bulblets are typically deeper.  Some people break down and use Roundup.  This might not work as Roundup works in hot weather and Oxalis is a cool-season grower.  Some folks sift their soil and get rid of the bulblets that way!  Besides being backbreaking, the bulblets can be pretty tiny and clay soils would be difficult to put through a sieve!  Even I'm not that crazy!

 
As far as I know, pulling the weeds out by hand before they can flower might help if you're tenacious enough or sheet-mulching every few years can help, too.  Sheet mulching is a back-saving way of taking care of weeds.  Simply throw down cardboard or layers of newspaper, making sure to overlap seams sufficiently and cover with at least 3" of mulch.  It works with the mulch to suppress the weeds, but also disintegrates after awhile and fertilizes the soil beneath.  You can't say that about that weed barrier cloth. 
Use unwaxed cardboard and be sure to remove any tape or staples.  I've also used this technique to remove lawns to great effect.  You get some funny looks, but it's an opportunity to teach your neighbors about more sustainable methods of gardening.
I however, have already mulched and planted my little bed and will hand-pick the Oxalis until I lose my resolve.  The spoils of this morning's battle are above.  Wish me luck and may Oxalis never find you!