[juvenal]

Whenever I lift a potato plant, I absolutely guarantee a tine of my fork will go straight through the middle of the biggest spud. It happens every time...

[grendel]

Start off well to one side and work your way in to the middle, this hopefully exposes the potatoes without going through them, then the next fork starts near the edge of the section you have just lifted, but in the area you have cleared the spuds already.
or start at the end of the row and move forward slowly, lifting the area ahead of the fork.

[JayG]

I use a large flat tined digging fork to try to ease the roots and spuds out of the ground without going too near them, pick up the visible ones, then use a border fork to search through the loosened soil for the smaller ones.

Works OK in my sandy soil, although I can't claim I've never speared one (and certainly can't claim I never leave any in the ground either!  )

[snowdrops]

I wish I could train hubby in those approaches , he just gets very grumpy when I suggest he moves further back from the row, I might not have said it that sweetly

[Tenhens]

Heard an idea the other day where you dig a trench and line it with weed supressant membrane. Plant the seeds , cover as normal. When it comes to harvesting ,just lift the membrane. Have not tried it myself.

[cadalot]

Next year is the year of the flower bucket and other buckets for my potatoes, the volunteers each year drive me crazy and no stabbed potatoes as well, easy harvesting.

[mumofstig]

A few other comments about forked potatoes here 

http://chat.allotment-garden.org/index.php?topic=121323.msg1430044#msg1430044

[Thrutchington]

I pull mine up by hand, no forking problems then.