I want to clarify this.

We all know that the genitive follows "ing", eg.:

looking for a man : ag lorg fir
doing work : ag déanamh oibre
annoying the boy : ag crá an bhuachalla
hitting his brother : ag bualadh a dhearthár

But... there's times when the genitive doesn't follow it. Here's one example where:

ag déanamh obair mhaith

It seems that where you have an indefinite noun, and where this indefinite noun is followed by an adjective (or a noun in the genitive), then you don't alter the noun.

But when exactly does this apply? Does it apply to the plural also?

Firstly, are all of the following correct?:

looking for big information = ag lorg eolas mór
doing good work = ag déanamh obair mhaith
praising a nice girl = ag moladh cailín deas (as opposed to "dheis").
hitting a small cat = ag bualadh cat beag (as opposed to "cait bhig")
seeking full-time employment = ag iarriadh fostaíocht lánaimseartha ( as opposed to "fostaíochta" )

What about some plural ones?

looking for small mistakes = ag lorg botúin bheaga?

According to standard grammar, after a verbal noun, the noun isn't in the genitive if it's indefinite (= without article, etc) and followed by an adjective or something that qualifies it.

Ag lorg botúin bheaga

BUT

Ag lorg na mbotún beag.

>>Ag lorg botúin bheaga

In this case, "lorg" behaves like a verb, and "botúin bheaga" is therefore the object of the verb. (Or rather: "botúin bheaga" behaves like an object, therefore "lorg" should be considered a verb.)

>>Ag lorg na mbotún beag

In this case, "lorg" behaves like a noun, and "na mbotún beag" is therefore the posessive phrase. (Or rather: "na mbotún beag" behaves like a possessive phrase, therefore "lorg" should be considered a noun.)

No wonder these are called verbal nouns...