How to set no "fast forward" as default when using git merge

Set the config variable merge.ff to false:

git config --global merge.ff false

(Without --global to limit the effect to the current project)

For anyone who wants to keep the fast forward on pull - you can override the merge.ff config for the pulls with the pull.ff config

git config --global pull.ff true

More info here: https://git-scm.com/docs/git-config#Documentation/git-config.txt-pullff