[Toughship]

Unfortunately i have a need to install some type of mechanical barrier in my exhausts to block muskrats from entering .  Googled muskrat guards and see a couple different styles are offered but they really work best with round exhausts .  My 3500 Open has oval approx 5 1/2 x 7
    Tiara does not recommend drilling and tapping the white end cap .  Warned that it is basically a molded gelcoat material 
that becomes brittle.  I was considering mounting a stainless laser cut screen on the outside.
  Wondering if anyone has a proven solution to this rodent problem?   Not allowed to trap or shoot the critters!