No, which is a better reply as your going to get, from the looks of things.

The guessing...

Try updating your graphics card drivers, and while Fences doesnt state a minimum graphic card requirements (none I can see) or gpu memory or GL version etc it is also likely your system is not quite compatible.

When you say "after using fences for a while" it indicates that some performance degradation on your system is going on, or your using too many applications at same time which may cause the slowdown.

idk just guesses since you dont provide much detail either.