set the minimum scale values for all layers in an mxd that don't have minimum scale values already set (the don't show out-beyond scale)

set_min_scales.py

#################################################################################
#
# Requirements: You'll need ArcGIS Desktop 10.1 or higher with Python 2.7 
#
# If you are publishing an MXD as a map service you might get a warning from
# the Analyze option that some number of layers "draws at all scale ranges".
#
# This script sets all the layers in the MXD you have open to a minimum scale 
# value of your choosing IF a layer's value is not set (indicated by being 0.0).
#
# It shows a list before the values were changed, and it lists them again after
# they were set. The lists are in layer_name: scale pairs.
#
# i.e.: Fire Hydrants: 10000.0
#
# Instructions: This is code you can copy/paste into the ArcMap Python 
# interactive console with the MXD open that you wish to review.
#
# You can paste it all, or you can paste a little bit at a time to modify what
# ever needs changing to your needs.
#
# Feel free to use, rewrite, and distribute as you wish.
# As always, use at your own risk!
#
#################################################################################

# set your mxd and get list of layers
mxd = arcpy.mapping.MapDocument("CURRENT")
lyrs = arcpy.mapping.ListLayers(mxd)

# output a list of layer: scale pairs to the console
print "BEFORE update: "
for lyr in lyrs:
    print lyr.name + ": " + str(lyr.minScale)

# set your minimum scale level (won't show out beyond)  
min = 9244648.86862
  
# set them if 0
print "\nAFTER update: "
for lyr in lyrs:
    if lyr.minScale == 0:   # remove this conditional if you want to change ALL layers
        lyr.minScale = min
    print lyr.name + ": " + str(lyr.minScale)