I recently made this handkerchief:
I didn't use a sewing machine for that one and just attached as I went. Like you, I eye-balled it. So if not with a sewing machine then I tend to do as you do and have made lots of handkerchiefs in the past with crochet edgings (not so much tatting then) and I always used to eye-ball it and push my crochet straight through the fabric as I went.
Otherwise, you could use a water-soluble marker and a ruler and mark little dots, evenly spaced.