Put a couple of pieces between them
Two Rooks

Technically, each rook "attacks" the square the other rook is in, but since they don't attack their own square, this is still correct.

You can put up to 8 rooks on an empty board without having them attack the same square.
What about 9 rooks?

Yep. For 9 rooks, do a 3x3 square.
The rooks on a1 and a3 both attack a2. The rooks on a2 and c2 both attack b2. etc.

You can put up to 8 rooks on an empty board without having them attack the same square.
What about 9 rooks?
Same problem as above (a1 and a3 both attack a2 etc).
I mean... otherwise you can place 64 rooks on 64 squares...
Like the eight queens puzzle, you need to place 2 rooks on the board. But not just anywhere on the board. The rule is that both rooks may not attack the same square.
How do you place 2 rooks on the board without having them both attacking the same square?