pregnancy announcement/Father's Day

So, I just found out that I'm pregnant but I haven't told my boyfriend. We've been trying for awhile to get pregnant and it's finally happened! Since Father's Day is right around the corner I'd thought I'd wait to tell him then! 
Do any of you have any ideas how I can announce it?
I've thought about putting a "big sister" shirt on our dog and just having her wear it around until he realizes what it's going on lol! Any ideas are welcome!