Tracking line annotations to footage

I have some footage of some smart phones demonstrating some software.
i want to anotate the footage.

i want to have the annotations were one end of the line 'sticks' to a tracked point. i have managed to do this.

i want to then make the other end of the line 'stick' to something else. im not sure how to do this with a shape layer with a path.


ive tried a lot of things!

many thanks for any help

----------------------------------------------------
studying computer animation at Bournemouth University (3rd year)
Part time DIT for RED and Arri film and commercial
----------------------------------------------------