Blocking revisions from auto merging in svn, taken from the manual.
$ cd my-calc-branch
$ svn propget svn:mergeinfo .
/trunk:1680-3305
# Let's make the metadata list r3328 as already merged.
$ svn merge -c 3328 --record-only http://svn.example.com/repos/calc/trunk
$ svn status
M .
$ svn propget svn:mergeinfo .
/trunk:1680-3305,3328
$ svn commit -m "Block r3328 from being merged to the branch."
