  Reconfigurable Intelligent Surfaces (RISs) are expected to be massively
deployed in future beyond-5th generation wireless networks, thanks to their
ability to programmatically alter the propagation environment, inherent
low-cost and low-maintenance nature. Indeed, they are envisioned to be
implemented on the facades of buildings or on moving objects. However, such an
innovative characteristic may potentially turn into an involuntary negative
behavior that needs to be addressed: an undesired signal scattering. In
particular, RIS elements may be prone to experience failures due to lack of
proper maintenance or external environmental factors. While the resulting
Signal-to-Noise-Ratio (SNR) at the intended User Equipment (UE) may not be
significantly degraded, we demonstrate the potential risks in terms of unwanted
spreading of the transmit signal to non-intended UE. In this regard, we
consider the problem of mitigating such undesired effect by proposing two
simple yet effective algorithms, which are based on maximizing the
Signal-to-Leakage- and-Noise-Ratio (SLNR) over a predefined two-dimensional
(2D) area and are applicable in the case of perfect channel-state-information
(CSI) and partial CSI, respectively. Numerical and full-wave simulations
demonstrate the added gains compared to leakage-unaware and reference schemes.
