Use a spot of Copydex every meter but away from turnouts and it holds the track but it can be lifted for cleaning point motors etc or adding circuit tracks if needed. I would avoid screws which I have never liked. C track is good and sits well.

Finish laying all your track before ensuring it stays in postion which it will with just a dab of copydex on the ballast every three or four feet. You can then easily lift sections when required.