I totally messed up the tracking on my car after taking the rack and ball joints off and not marking stuff first.
I made one out of a length of straight wood with 2 right angled shelf brackets fixed on at the end, each with a bolt through at the top end (to provide fine adjustment by changing the length of the bolt)
get the car level first, and then the wood sat flat on the floor, then the shelf brackets stuck up at the ends and the bolt was adjusted till it touched the inner rim/edge of my wheel.
I think i went for a tiny bit of toe in on my car so i had it so my bar fitted in at the front and had a bit of slack at the back.
Takes a while but seems to work roughly. later checked with a gunsons trackright and thet thinks i have equal toe in on either side.
Ive not got round to taking it to a proper garage to have it chcked yet but hope to in the next week or two.