Triggering layer

Hey,

Not sure whether I posted this before, but I am once again stuck with this conundrum:

I have 4 layers. When 3 of them have been visited, I want the 4th layer to show. 

I have tried this:

1. Placed variables that will change when layer have been visited (when timeline end son that layer)- on each of the 3 layers.

2. Created also a fake object that will complete on all 3 layers to trigge rit on the 4th layer.

I can't seem to link either of  my 2 options on this 4th layer nor the base layer.

Any ideas?

Thanks!

Kai