DODS/Rocket targets
filter_damage_type instead, since it would likely be a much more foolproof way of doing this.A tutorial on how to make a wall that can only be destroyed by rockets or grenades.
Make a Brush
Create the brush for the hole that should remain after the wall is destroyed, then create the center piece of the wall. On the wall there should be a visual aspect that will let players know that it can be destroyed. A similar technique to the DoD 1.3 maps, with 3 cracks in a "Y" Shape, can be used for instance.
Configuring the entity
Select all the parts of the wall that will be destroyed, and press the Tie To Entity button (Ctrl + T). Set the entity as a func_breakable and change any other values should they need to be different. The only keyvalues that need to be changed for this tutorial are the Strength and Min Damage to Hurt values. Since the Kar98 and Springfield snipers both do 120 damage, the Min Damage to Hurt must be more than that. Rockets generally do 125 damage, so set Min Damage to Hurt to 125. The strength can be anything, though it is recommended to be 125 times the number of rockets you want to be needed to break the wall.
Problems
Rockets may not always do enough damage to surpass the 125 damage needed to hurt the wall, in this case filter_damage_type could be used as an alternative method.