haha i had exactly the same problem- took me 3 months to convince my dad. Have you tried Bargaining? Thats what i did, my dad was up-tight about it being a "gun" as well. So what do ya do?
1) you'll never use it in the house(if you did you'd b stupid any way)
2)Put it some where safe, i have mine in a metal box lined with foam. Ever herd the frase "outta sight, outta mind"?
3)And if those and what the other guys av suggested doesnt work- there's always bribary. Lol
Gd luck m8
daz