About the only thing you can hope to accomplish is preventing the state from successfully asserting that you gave consent for entry/search, or that you voluntarily surrendering the contents rather than had them confiscated.
The "explosive material" warning could actually give cause for an exigent basis warrantless entry - public safety, fire code, etc. and defeat the purpose of the warrant required warning.
That warning is lacking in several respects. Here is a better one:
LEGAL NOTICE to POLICE
This safe is the personal property of <name>. It is not shared property with any other person.
Consent for police entry or search is NOT GRANTED. No person other than <name> may grant consent to enter, even if such person has the combination to this locked container.
Entry by another person at the request of police to effect constructive entry is also prohibited.
The surrender of the combination in response to a police or court order shall not be considered consent to entry or search of this container.
This notice shall also serve to establish that no “verbal consent”, “implied consent”, or consent based on “power of attorney” shall be valid. Consent must be obtained in writing from <name>.
This notice shall also apply to any locked gun cases stored in this residence.