blokking backlink scrapers from my site

Hi,

I would like to block all back link scraps zo my competitors can not scrape my backlinks.

I would like to blok atleast majestic seo and ahrefs
also i like to block webmeup and seo spy glass.

I think i only nead to add some code to my robot.txt file ???? if zo who can copie his code over here zo i can copy past it in my robot.txt

I can probaly goole this only im lazy at the moment