Surface plasmon resonance (SPR) and guided wave SPR (GWSPR) are widely used in sensing. Efforts to improve the sensitivity and stability of these sensors are done by using different multilayer nanostructures such as with the long range SPR and the use of combinations of materials such as gold and silver. Silver based SPR sensors have high sensitivity but a poor stability because of the interactions with water and air. We have shown both theoretically and experimentally that by using the silver based SPR sensor with a 10-15 nm top layer of dielectric film with a high value of the real part ε′ of the dielectric function, it is possible to improve the sensitivity of the sensor by few times. The imaginary part ε″ of the top nano layer's permittivity needs to be small enough in order to reduce the losses and get sharper dips. The stability of the sensor is also improved because the nano layer is protecting the silver from interacting with the environment. The calculated evanescent field is enhanced near the top layer - analyte interface, thus the enhancement is due to this and due to an increase of the interaction length as a waveguiding effect.