Changing clip length but keep the effect keyframes stuck to the end

[SnrDiggan]

Hi,

I am driving myself mad as I have already done this but cannot remember or find out how to do it again. 

I habve created scale keyframes for a png logo in the effects control at the end of a clip. When I change the length of the clip the keyframes stay at the same time point. I know there is a way of creating a 'zone' on the effects control time line at the start and the end so when you change the clip length it only changes the time between the two 'safe zones'. 

Please can anyone help me and show me how to do this?