Ion temperature clamping -- the saturation of the ion temperature regardless of heating power -- is observed across stellarator experiments. We propose a minimal model based on Anderson localisation. Starting from a reduced fluid model for drift waves [Phys. Fluids 26, 880 (1983)], we show that aperiodic stellarator geometry leads to a quasiperiodic Hill equation for the ion-temperature-gradient (ITG) mode structure. In a tight-binding approximation this equation reduces to an Aubry--Andre--Harper difference equation, suggesting an Anderson-localisation mechanism for ITG eigenfunctions. We identify a three-threshold ordering: the linear instability threshold lies below the Anderson localisation threshold, which lies below the observed clamp. This is conjectured to create a low-transport second regime above the instability threshold, qualitatively analogous to the second stability regime of MHD ballooning theory, and provides a power-independent lower bound on the observed gradient.