One way would be to use a secrecy deck (the new Glorfindel makes this easier). I, however, try to use as many 5 HP heroes as possible, but one can also handle this if you have enough healing cards. Boromir and Loragorn make a nice duo in this scenario. My strategy is not to defend Striking Tentacle, because as you said, in most cases this won't help anyway. Then I kill the tentacle and try to heal the damaged hero with DotN (she's more effective in this scenario than Warden of the Healers).
Frodo also helps.
Another strategy is to use Hail of Stones or a combination of Thalin, Fresh Tracks and Gondorian Spearman.
If you just want to delay the attack (to play Gandalf next round, or to use Dunhere etc) there are cards like "A Light in the Dark" or "Out of Sight".