we have it (2 actually

) and what we did was tuck it behind something heavy on both ends (when it wasn't in its shape, when it was out in a line type form) and Seamus' couldn't knock it over, he did learn to climb over it just after he turned 2 though

We dont have a gate at the top of our stairs because of Seamus, dh is scared he'll try to climb over it and fall down them