I still struggle with tones, mainly 1 and 4, it's really difficult

As to your example 小狗走在沙灘上, I think (but not 100% sure as my Chinese isn't exactly perfect) the emphasis can be on 小狗， 走在 or 沙灘上 to show the emphasis in the sentence. The weight of the prononciation would be slightly heavier and I'd probably pause a little after the emphasis. But as I said, my Chinese isn't perfect so if I were you I'd take what I'm saying with a pinch of salt. 😁