Replace Toxic Spikes with Volt Switch.
It will do near nothing damage wise, but it'll keep momentum. Toxic Spikes is okay, but if your opponent has a Poison type (which are all the rage these days because of Fairy), then the Spikes will be absorbed and will be useless.
Volt Switch is also good on Forretress because it's slow, so if you have confidence in its defences, you can see what your opponent will do with their Pokemon and then Volt Switch safely out into something else without your next Pokemon taking a hit.