Get in touch with SteelSeries and get replacement grips for your Rival mice.
The Rival 600/650 gaming mouse from SteelSeries is an excellent mouse, but it's let down by poor adhesive on the sides that hold the finger grips in place. When the mouse is exposed to high levels of heat from the environment or sweaty hands, the adhesive starts to heat up and allow the grips to slide around, causing quite the mess. Luckily, SteelSeries is aware of the issue and can ship out replacement grips for you.
Full story from the WindowsCentral blog...