Ahhh your user name is Motion, but you were inquiring about Keynote.
What Mac OS version are you using? And what version of Keynote are you running?
You could lock the Keynote file by changing the permissions on the file.
Navigate to the Keynote project file. Then press Cmd+I. This will bring up the information box for the file. Navigate down to Sharing & Permissions.
Unlock the lock on the bottom right. You will be asked to enter your password. Change all the users under the Name column to Read Only.
Now if you pass this file onto others they will only be able to read the file, not change it.
Unfortunately this is not a full proof solution. If the user knows how to change permissions on files, they'll be able to add full access to the file again and modify it.
I hope this helps a little though.