Pentience, i believe is what its called (The single damaging move). It can cause the good damage when he moves in range to do the acid spit. It also does something to the demi god like slow it down and make it take more damage, if im not mistaken. Also quickly pressing 'm' to select your minions and right clicking on him can send them after him.

This is called harassing and it's a lovely tactic. If done correctly, you waste more time keeping yourself alive while he creeps and pushes. To counter it early game, I'd honestly get a buddy to gank him or switch lanes with a ranged demigod who can harass back. Queen of Thorns is a great counter to UB harass, her shield makes his spit useless and her ranged attack + minions can harass him all day since he is melee. Reg is good at this as well if he watches for the spit.

In your case, I'd stock up on +speed gear (or wand of speed, pop it for 25% movement) or find ways to slow him down such as the gloves that have a chance to reduce movement by 15%. Once you are next to him you can probably kill him. He's a tough melee fighter though so I'd be careful.

Also, don't forget you can use your minions to harass back. It's a very useful tactic.

I was thinking about adding the single target spell to my build just haven't figured out where to fit it in yet since i do love hitting people with that as they run away.  

The shield i have actually never used but i guess i should try  that and see how that works.  From reading these replies i think i need to learn to be more flexible in my build and not be so anal about it  . 

Thanks for the help, if anyone else has any suggestions please put them here. 

Oaky with no Shield?

Are ye daft, son?

(Constructive criticism, Oaky is a defensive powerhouse.  Learn to love his defensive and debuffing abilities to allow you to counter and then press the offensive advantage.)

Shield -> harass, retreat.

Rinse repeat for maximum effect.

Pentinence is an awesome skill, but if you dont want to, you can live without it.

I play Beast and the only thing that I have to run from when fighting Oak is if he puts up his shield. Unclean Beast is all about burst damage. He will spit on you and do one of two things.

If he spits on you and runs away, do not follow him. You will die. He's recharging his mana and his spit. He will spit on you again but this time he'll come in for the kill - and if he's worth his salt he will get it.

If he spits on you and roars, he's probably coming straight for you. This is where Oak shines. You are about to take a retarded amount of burst damage. Hit shield and it won't happen. Simple as that. The Beast will have his recharges up and more than likely will not have any mana left since Beast doesn't have that much mana typically. Usually they have enough for one "hit" on a hero, and then have to regenerate their mana. When he sees your shield go up he will retreat to gain mana. Once you see his health start going up hit him with Pentinence - this will interrupt his Heart of Life. You now have half a minute to destroy him because he has nothing to throw at you.

There is one final option - and if this happens you will have a fight on your hands. If he comes straight at you, you shield, and he breaks off the attack immediately without wasting any mana - he's a smart Beast, and when your shield drops you will both be on even footing.

i played a game with this oak guy, he was pretty good.. he had the best favor item in the general tree..the one that heals u for 2000.. he used to shield himself and use that heal.. this is before i had foul grasp because he could do it at level 1

anyways.. he kept whining about how op spit was.. yet even if i got him down he would just stand there, shield and be at full health.. people these days lol.. find a reason to bitch about everything without realising what the other person is going through

Ah, the Unclean Beast. My bread and butter.

The Unclean Beast is all about harassing! He cannot really tank damage for beans; he's made to finish off wounded demigods and waves of creeps. When I'm on playing the UB, I am roaming the map taking back flags. If I see an enemy DG or two fighting a teammate, I will usually come in, Spit on whoever my teammate is fighting, and move out- but not far. I circle around, spit, and if I see the chance for a kill I move in and melee. If I see the Queen's bramble shield go up, I don't even bother attacking as it's just wasted mana. If I see Oak, I definitely do not go toe to toe unless he is already hurt. If it's the Rook, I only jump in if he has his back turned. The advice you are getting is right; the best thing for you to do is to react before he does. 

Interrupt him before he can spit on you, or shield yourself just before he does. If you manage it, you've negated a lot of his damage already. If he gets a surprise "from behind" Spit off on you and then you see him roar, you're better off interrupting him and then getting away. That roar adds 25% weapon damage to him and, if he has a pile of +attack speed gear on, he is going to shred you. Big time.

You can beat him, but not by just plainly outdamaging him. You have to pull a Muhammad Ali-style "Rope-a-Dope", i.e. take or prevent his initial huge spike of damage, then counter-attack. Sounds complicated, but it's quite simple.