I've seen people use a painted pallet/half pallet with a cluster of medium and large statement-y pots on it to disguise a manhole cover. Means that it can be easily lifted if you need access.
I'd echo pp by adding a few more slabs to even the patio out. Maybe just one more row or a couple more slabs if you still want an irregular shape going into the lawn. Looks a bit odd with that square jutting out! Saying that I can't tell how far the patio extends back to the house or if there are more slabs lurking under the grass
Feel free to ignore if you already have lots of patio. I like the look of the image you attached!
Do you know anyone with a pressure washer you could borrow to blast the slabs clean? Not urgent but it usually brings them up nicely.
If it was my garden I'd probably want some long/tall/narrow wooden raised beds (e.g. 40-60cm wide and high, 1m+ length) at the edge of the patio/lawn. The sunny side definitely but possibly both sides in due course.
They're an outlay initally (factoring in the compost) but it means you have a nice tidy area to plant in, not so much bending down, out of reach of the dog/baby, able to control soil quality etc.
The alternative would be to dig a border (effort, dog/baby destruction, need to keep lawn edge trimmed) or have pots on the patio. Pots are fine but you really need decent sized ones for root growth/prevent drying out/avoid tripping over them 
Everything looks better with a tidy lawn, good luck!