Strainers are deadly obstacles best avoided. When you notice one, decide whether you can quickly swim out of harm's way. If you are holding on a boat, consider pushing off the boat for better cross current speed. If unable to avoid, paddle very aggressively into and over the strainer. Be prepared for quick climbing on branches and avoid the temptation to dive underneath. Trees have snags that can hook onto your PFD or clothing creating a death trap. Just remember, what you don't see can kill you.
Holes can sometimes be avoided or skirted. When you enter a hole, be prepared to go underwater very quickly. To avoid foot entrapment, tuck into the cannonball position. If recirculated, time your breaths for when you surface and be prepared to catch a throw rope if tossed your way. Consider adding some momentum to your next dive to swim out of the bottom of the hole. If that doesn't work, perhaps you can to a break in the hole or one of the ends. Finally, try changing your body shape. Swimmers are generally poor hole bait (unlike some boats). Elongating your body can sometimes cause a hole to reject you. It is also important to conserve your energy and make carefully planned moves to avoid flush drowning.
Take great care going over large ledges. The bottom of these ledges can be foot entrapments. This is where the tightly tucked position is really important. The tucked position also protects the soft portions of your body, especially the face. If recirculated, follow the same guidelines in the previous paragraph on holes.