Scoutleader,
If you can, get one of the peepholes that has a cover flap on the inside of the unit. This way, you can be in position before opening it and the subject outside will not see the light "dim" in the outside lens and know when to kick the door into your face.
In addition, if you haven't done so already, replace all the screws holding the hinges, striker plate, deadbolt and chain-locks with longer screws. The longer screws take more effort to pull out or defeat.
With summer coming, secure your windows and sliding doors too.
First Alert sells small battery operated alarm units for windows & doors. These will let you know that someone has opened or moved a sliding window or door. For sliding and sash windows, install a piece of aluminum "U" channel in the track to prevent the window from being opened more than you want. You can cut it "short" and add short sections to adjust the window's opening. Combined with the alarm units, this allows open windows on summer nights with some security.
For louvered windows (such as in some bathrooms) be sure the glass panes cannot be easily removed. Seal them in place with a few spots of silicone sealant.
Below ground level windows, plant thorny bushes like Roses or pyracantha to discourage access. If that's not an option, use crushed rock or "lava" rock in 18" wide beds under the windows to add a loud crunching sound. Motion sensor lights on concealed sides or back of the house also deter nighttime sneaks.
Sometimes just a simple sign will work without all the added expense...