Using aliases in `~/.bashrc` rather than putting scripts or symlinks in $PATH is a good mean to avoid those kind of problems, provided bashrc includes code to quit if ran in non-interactive mode (default at least on ubuntu).

Many use aliases only to specify default command parameters, but it works just as well to provide an execution path, like, in this case:

    alias df=/home/my_user/games/dwarf_fortress/df

It would only be executed in interactive sessions, this way, which should guard well enough against system code interpreting it.

Of course, this still means user can't use system's `df` easily, but I guess they don't use it anyway since they did not realize the problem until that upgrade.