Apparently in the guide it says 49 grass blocks and 49 rock blocks. Don't know how long you wait but I tried 7 blocks for 250 days. I'm crazy yes I know but its equals perfectly 49/7 equals 7 so yea but I havent caught one yet sorry
How To Get Gible In Pokemon Heart Gold?
They say you can do 13 plain blocks and 17 peak blocks in the safari zone and wait 100 days, and it'll appear but it didn't for me, all I got was a zangoose.:/
Its bs you change the safari zone to dessert and wait 1 day and gible will apear I tryed and it workedfor me =] hope it helps if not sry =\ because my friend tryed and it didnt work =|||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||(long chin awesomeness) =}