assuming deep stacks and 4-6 players in the hand, how would you play these? let's say you have 79 or 88 on a 789 board with 2 diamonds. My initial impulse is to bet (pot size at least) to protect your hand, but I'm thinking should I check this instead and play this as a small pot? Of course you have outs to a fullhouse if a potential flush or straight card hits on the turn, but doesn't this thinking actually show how vulnerable the hand is?

There isn't really enough information here to make a good decision. Is everyone in the hand deep stacked? What position are you in relative to the preflop riaser if there is one? What are your reads on your opponents and them on you? Also stakes matter to know the level of competition you are potentialy against. .01-.02 and 1-2 not the same level of player so answers will change.

The answers to these question can drastically change the answers you are given for any hand. That is why we usually ask for specific hand examples.

My general answer would be that you have a strong hand and it is worth betting for value, not to "protect".

also are we talking about a ring game or a tournament . if a tournament how far into the tournament are we when this hand comes up

Like said above, not enough information to go on.

For what it's worth with 2 pair hands on a scary board in a ring game, I like to bet fold. Bet just over half the pot, if you are called it is likely they are on a draw, if you are raised it is very likely you are beat.

It is possible to get raised by a draw, but that all depends on the opponents and the situation, which is why more information is needed. The more information you have/ and use, the better decision you can make.

on that board, with that many people in the hand. i think i would check if i was frist to act. see how the action plays out, and play the hand for as cheap as you can.

if you have a PP you should raise preflop to reduce the number of players in the hand. so with 6 people in the hand, this must have been a limped pot. which you want to be careful in a limped pot.

so raise your PP 4x, and add a big blind to your raise for every limper in the pot. this should help with not having so many people in the hand.
plus it will hide the strenght of your hand. i am talking about ring game play and not tournament play. in tournaments alot of what you can do depends on the size of your stack.

hope this helps.

Your example doesn't match your question. You're acting as if you're sure you're good, despite the fact that a flop of 789 isn't just a drawy board, it's a board where a straight has already hit. If you want to talk about 782 or something, that's a different story, but right now, I would just play a small pot because you can't be sure you're good now, and if you are, you probably won't be for long.