The Laser fence was an advanced Nod defensive structure. Basing on their signature laser technology, the "fence" was essentially a network of highly effective pylons, which were capable of creating an impassable laser barrier between them, denying access to the interior of the Nod compound.
The first registered application of this technology was during the First Tiberium War, when prototypical laser fences were set up in important Nod bases as advanced defensive structures. The Cairo Temple of Nod was also protected by a high power laser defence grid.
In the Second Tiberium War, the laser fences became an integral part of the defensive systems of Nod bases, but the weakly armoured nodes and massive power requirements of the network were a significant drawback of the technology.
By the time of the Third Tiberium War instead of surrounding an entire base, the beam generators were used so that they would surround a single building at a time, increasing its armour and protecting against engineer infiltration or sabotage with explosives. In Kane's Wrath, it was deployed from the Operations Center, with each building requiring 500 credits to protect.