I have an arkose 4 and have used PDW Full Metal Guards and I’m currently using SKS Bluemels guards. The under fork mounting is a bit of a pain in the arse but it is nice and neat. When I fitted the pdw guards I put an L bend in the bracket on the guard then drilled a hole through the guard to access the bolt, this made no difference to water getting at me.
With the sks guards I just put the under fork bolt through the fitting, tightened it up, with a rubber washer between fitting and fork, then just moved the guard into the right position thus bending the mounting point. Works fine. Wouldn’t want to do it if I was taking the guards on and off regularly but it’s my winter/wet day bike so I leave the guards on all the time.