On discovering that Pat was pregnant, the couple needed to find a suitable house to live in, and they bought a house at The Villas in Stoke. Arnold used a long, narrow greenhouse for his studio, and Pat had a room at the top of the house as hers. They made Stoke their base, and Arnold would drive down weekly to London where he kept his small studio on. Their son, Francis, was born in November 1949.

Arnold enjoyed teaching at the RCA, and he would insist that students be honest with their work, encouraging them to draw sensitively with a searching understanding of what they were doing and with no fashionable gimmicks.

In 1951, Arnold was approached to teach modelling part-time at Derby School of Arts and Crafts, which he did so one evening a week for nearly four years. In February 1956, Arnold was elected a full member of the Royal Academy of Arts. His Diploma Work, which he presented to the Academy on his election, was a terracotta entitled 'The Fallen Angel' which was displayed at the Summer Exhibition in 1957. In 1958 Arnold was invited to put his name forward for a vacancy at the Royal Academy Schools and he was elected Master of Sculpture in 1959. Although the salary was negligible, Arnold did have a private studio which was heated and lit free of charge and was therefore a valuable asset. A colleague of Arnold's at the Academy had established himself at the studios in Sydney Close, and the one next to his had become available. The studios at that time were owned by the Smith's Charity Trust and Arnold had to be interviewed to ensure he was a suitable occupant before he was able to take it over. The rent was very reasonable and the space huge – about 25 feet high – so an excellent find for an artist.

Whilst at the Royal Academy, Arnold stuck to traditional teaching methods and taught stone carving, woodcarving and life-drawing in whichever medium students preferred. Students were also encouraged to visit places of interest, particularly locally as there were so many sculptures to see in London. The Royal Academy had an excellent library, and students were very much expected to get on with their own work and develop their own style with advice and suggestions from their tutors. Sir Joshua Reynolds had said to his students, “We can teach you here but very little, you are henceforth to be your own teachers”. After Arnold had been at the Academy for about three years he had about fifteen students in the Sculpture School and at the end of the diploma year they put on a huge show of their work, but unfortunately it had very little response from anyone, and it was then that Arnold realised that Modern Art was taking a stranglehold on their endeavours.

It had long been a tradition that the Scottish Schools of Art had their students' work assessed by outsiders, and as Master of Sculpture at the Royal Academy Arnold was appointed as Visitor to Glasgow, Edinburgh, Aberdeen and Dundee, and would visit annually to make a final assessment of the work of the sculpture students.