The arms
This is the one shield the family actually has, and everything below is what's actually known about it, including the parts nobody can fully explain.
Registered: 28 April 1978, South African Bureau of Heraldry
Registered to: the Van der Walt-Familiebond (the family association, covering every van der Walt)
Blazon: Quarterly Azure and Or, a demi-eagle displayed Sable, a fleur-de-lis Or
Replaced: an earlier design shown in 1975 to belong to an unrelated Frisian family, Walta
Not registered (personal only): helm, wreath, motto
One shield, registered
The shield is the family's own, registered with the South African Bureau of Heraldry on 28 April 1978. The black half-eagle on gold is for the family's Frisian origin. What the gold fleur-de-lis on blue was meant to represent, the record doesn't say, more on that below. That is the whole of the registered arms: a shield, and by law nothing more, for a family association may register no helm, no wreath and no motto. So the shield stays fixed and shared. It doesn't change.
What changed in 1978
For generations the family bore a half-eagle and three silver lozenges, believed to be old and theirs. In 1975 the genealogical authorities, the Centraal Bureau voor Genealogie at The Hague and Dr C. Pama at the Cape, established that those were in fact the arms of the old Frisian family Walta, carried in good faith but in error, with no proven descent. The Bond set the old arms aside, and in 1978 registered a corrected shield: the eagle and a single fleur-de-lis, with no lozenges. Why a fleur-de-lis, specifically, no surviving record explains: the Bureau's certificate confirms the blazon it registered, not the Bond's reasons for choosing it. The family chose accuracy over flattery.
The wreath and motto: yours, but personal
Everything around the shield, the leaves of the wreath and a motto of your own, is personal embellishment: not part of the registered arms, a personal device, freely given, that makes no claim upon the Bond's registered shield. You are welcome to it.
The three lozenges
One line brought the lozenges back, not as Walta's, but as their own. On 19 February 1896 the Braamfontein dynamite explosion took, from that direct line, a mother and her three young daughters: Anna Sophia van der Walt, born Steyn, and her girls Hester, Johanna and Dauwlina, then about fourteen, five and three. The three lozenges are the three girls. A charge that once came to the family by accident was restored on purpose, and given to them.
The charge came by accident. What it now carries did not.
What this means for you
Your shield is the registered family arms, the same for every van der Walt. Your motto is yours to choose, and anything more you add is your own mark, claiming nothing it shouldn't. You may have seen "Van der Walt family crest" items for sale online: those aren't this shield, they're invented, with no genealogical basis behind them. This one is real, registered, and already yours.