1.Rg1?

1...h3 2.Sg8! ~ 3.Sf6 (+) ~ 4.Rg4#

1...Sf7 2.Sxf7 h3 3.Rg5+ Kh4 4.Bg3# 

but: 1...Sg6!

1.Rf1! threat: 2.Rf5#

 1...h3 2.Bg3 threat: 3.Rf5#

                2...Sf7 3.Rxf7 ~ 4.Rf5# 

1...Sf7 2.Rxf7 threat: 3.Rf5#

             2...h3 3.Bg3 ~ 4.Rf5# 

Change play to 1...h3 & 1...Sf7. Playing on the same square.