Canadian Tire Premier Fit plastic splash guards, $11.99 a pair (so about $24 for 4):
http://www.canadiantire.ca/en/pdp/pr...8817p.html#srp
That was about 2 years ago when we first bought the Little Guy, so far they're doing a great job of protecting his underside from rock chips and other debris (we did some light off-roading with him in Death Valley in Feb 2017). They are still quite secure, no cracks or rips, a little dirty but hey they're splash guards...
My only complaint is that because they're rigid & not flexible, be careful what you're climbing over (scraped them a few times on curbs but they still haven't fallen off)...
We had one of the techs install them for us while Little Guy was up on the hoist for an oil change, used the existing pre-existing screw holes in the front fenders and drilled holes in the rear bumper for the back ones...